Unfortunately, SAM has ruined Steam achievements for the world, to the point that they are useless and prove nothing anymore. (I don't care anyway but ya'know.)
http://steamcommunity.com/id/zeke01/stats/L4D2?tab=achievements And I'm sorry that the Society of American Magicians ruined achievements for you. (Yes it is a real society)
... proves nothing. Here you go: http://steamcommunity.com/id/OMGDANTE/games?tab=all I have every single HL2, EP1, EP2, Garrysmod achievement. You think I did them? No. But they are there. Look at the time played for the games. Derp derp, im going to bed.
Zeke has an OCD for legitly earning achivements. If he earned them, he mostly likely did. The same how he owns a fucking ferrari which he has yet to borrow to me.