I'm no expert on guns in the mechanical sense, but I'm very into 2nd amendment issues and read up on the matters often to make sure I can articulate my position. After doing some research, I found the Dragunov Sniper Rifle (Russian: Snayperskaya Vintovka Dragunova) and will use the Russian derived acronym for this discussion.
As stated in the Wikipedia article, it has several features in common with the AK family (more on this in a second) that would lead the uninformed (sadly, pretty much any politician that does not like guns... who are the ones writing these laws most often) to mistake them for an AK family rifle, despite these features being largely cosmetic (and often "Scary looking") to the the uninformed politician. This is fairly common in Gun Legislation as the US's 1994 assault rifle ban (and all attempts to re-enact it) had a number of guns that were listed solely for cosmetic reasons or were not allowed to have certain parts attached to the gun for the same reasons (And in some cases, the feature did make the gun look scary but served a vital function that would see notably diminished capacity in the gun it was attached too. In a few examples, the banned attachment was a safety feature meaning that the gun was more dangerous when it looked "Safe" than it ever was when it was "scarier").
The effect of the law based on false facts is negligable. There are lots of laws passed that are based on lies, false data, misconceptions, ect. and just because they are bad faith does not make them illegal. They are still laws. Similarly, even if you say the SVD was miscatogorized into the AK family of weapons, it doesn't negate the fact that the law's purpose was to stop the listed guns from being legal to own firearms, even if they made a mistake as to where they put it. From what I know of the general attitude towards guns in Canada, and the general attitude of the people in the States who make similar legislation, it seems like they intended to ban all these weapons individually and classified the SVD incorrectly.
The reason that this happens is because, while these legislators don't know much about guns, they know a lot about miltary grade weapons sales to know that gun varients happen often and generally in a few different ways. It could be that a country with a strong arms manufacturing sector (like the U.S. or Soviet Union) will enter into deals that sell arms to an ally in exchange for money into their economy and intel on the weapons stock. It's easy for the U.S. to know how many tanks a nation has if it has the bill of sale. Often, to get some people back home happy with him, the purchaser will ask if they can make the weapon themselves, with assistance from a handful of in the know seller nation engineers and a lot of their own workers filling out the rest of the manufacturing roles. The other reason is that enemy nations secured the weapon and want to make their own, both for training against it OR because it's so good and they cannot buy it. The AK-47 was subject to both reasons as the Soviets widely sold it to their allies and the US widely stole it because they wanted to know what made it work AND it was better than the US standard issues... so it got this treatment a lot. (The third option is that of the AR-15 and similar rifles. The AR-15 is quite popular in the U.S. and the copyright on the manufacture of the weapon has lapsed. There are a number of gun manufacturers that will sell AR-15 like rifles but under a different name because AR-15 is still a trademark name, even if the design is not, and the derivative rifle maker can be sued for trademark violation.).
Suffice to say, since legislatures do deal with these matters a lot, as they typically approve of all sales of arms to other nations, they do understand this concept very well, even if they are not in favor of civilian gun ownership. It's likely they assumed the SVD was related to the AK-47 and did not want to write it out as a seperate model and didn't check. Thus, they intended to ban a lot of vehicles, including a locomotive and a Mustang, and for some reason thought that the Mustang was a locomotive and put it there instead of with the list of cars. If you find it a stretch to believe, go look at the questions asked by the various sub-comittees to the CEOs of tech companies and then tell me again the mistake you're asking about is not the dumbest thing ever to happen in a legislature.