My assumption is it just falls back on Helvetica only when using an Apple computer or computer with Helvetica already installed. This is what happens with web fonts that use Helvetica.
From what I'm reading it doesn't use Helvetica at all, it uses Nimbus Sans which is just very very very similar to helvetica but its not identical.
In this link it says:
• Nimbus Sans (i.e., Helvetica)
Which I'm pretty sure just means it's a replacement for Helvetica.
As far as the law is concerned...
In the USA it's hard to say. I can give a few examples here for you to research.
URW++ was involved in a 1995 lawsuit with Monotype Corporation for
cloning their fonts and naming them with a name starting with the same
three letters. As typeface shapes themselves cannot be copyrighted in
the United States, the lawsuit centered on trademark infringement. A
US court decided that Monotype's trademarks were "fanciful" and did
not have descriptive value of the actual products. However it also
decided that URW was confusing the public deliberately because "the
purloining of the first part of a well-known trademark and the
appending of it to a worthless suffix is a method of trademark
poaching long condemned by the courts." The court issued an injunction
preventing URW from using their chosen names.
I'm not a lawyer but I can site this case. To explain why "Font shapes are not legally protected," might not be the correct answer.
A legal precedent was set in the case of Adobe Systems, Inc. v.
Southern Software, Inc. (SSI). SSI had used the FontMonger program
to copy and rename fonts from Adobe and others. They assumed
safety from prosecution because, though they had directly copied the
points that define the shapes from Adobe's fonts, they had made slight
adjustments to all the points so they were not technically
identical. Nevertheless, it was determined that the computer code
had been copied.
and also take a look at