But now you know that this "free asset" is from another game, and is not a "free asset" actually, just somebody ripped it from the OG game and published without sourcing. But now you know the source, so you could just, you know, add this tiny bit of info to the game page. Dunno what's so weird about it?
The fact that your old game was stolen, retitled and republished is of course abhorrent, no question about it.