In the US, "insider trading" includes both legal and illegal versions. When a corporate employee buys or sells shares of their company, they are insiders and they are trading (there is a requirement to report to the government). The illegal version involves breach of fiduciary duty or confidence. The relevant section of the federal regulations is 17 CFR 240.10b on "Manipulative and Deceptive Devices and Contrivances", and you will note that the section does not rely on the term "insider" in the law part, instead it directly characterizes what acts are illegal. Thus it would not matter, from a legal perspective, if someone considers you an insider.
It is illegal to trade in securities using a “manipulative, deceptive, or other fraudulent device or contrivance”. This relates to what is commonly known as insider trading via rule 240.10b5-1, by defining as manipulative and deceptive trading
on the basis of material nonpublic information about that security or
issuer, in breach of a duty of trust or confidence that is owed
directly, indirectly, or derivatively, to the issuer of that security
or the shareholders of that issuer, or to any other person who is the
source of the material nonpublic information
(emphasis added to focus on the core requirements). Whether or not you have a "duty of trust or confidence" is determined by common law standards, that is, it depends on how courts have ruled on similar matters. For instance if the CEO of Apple tells you "Our computers explode and it's gonna be on the news tonight, the stock is gonna tank, but it would be illegal for you to act on that information", then it would be illegal, because you are aware that the CEO has a duty to not use that information (thus you "inherit" the duty). This also holds if he doesn't tell you that acting on the information, since it is expected that you know that the CEO of Apple could not legally act on that information (even if in fact you are unaware of the law -- ignorance of the law doesn't get you anywhere good). However, if you are unaware and could not know that the person making the factual disclosure is divulging information that he has a duty to shut up about, then you might not get prosecuted.