It would be stupid of someone to buy something and not know what its purpose. You don't accidentally buy BTC because for someone nowadays, BTC is too popular. And if you did buy even just a fraction of it, you know your purpose and its either for your investment or you wanna gamble.
I know one kid buy BTC just to impress his IG followers that he is into BTC. Now thats one heck of a purpose.
I think it's quite normal for people to not be aware of bitcoin, even in this world where crypto is wildly adopted and there are tens of millions of people who use it, there are still billions who have no idea about it as well.
However, I do agree that it would be pretty difficult to mistakenly get any, it's something that requires a lot of work to get, I mean not a lot of work but certainly not easy enough that you will mistakenly get it. Even in fiat there could be someone who dropped money on the floor and you could pick it up and mistakenly have money, crypto doesn't even have that. So short story long bitcoin is something you want to buy if you want to get it, that instagram kid definitely did the right thing, I hope he keeps it after showing it off.