Assuming that Eugene isn't just a Trekkie spouting enough technobabble to sound plausible.
I think that's exactly what he is. Or more accurately, a gamer. When he spouted gamer lingo, the intent could be for us to think "Scientist geek = lots of gaming in his spare time", when in reality it's the opposite: "Expert gamer = lots of spare time to read up on science-y stuff".
Before the ZA he probably mastered some minor online game that happened to be about Romero-style zombies. That sort of fiction may not exist in the TWD universe like it does here, but that's not to say it doesn't exist at all. This would be something so obscure that maybe one person out of 50,000 would know about it. (If we assume the non-zombified world population is down to, say, five million people, that means only a hundred people worldwide would still remember it.)
So Eugene was one of those few. Maybe he and some of his gamer friends in D.C. are tech-savvy enough to manage a satellite phone connection, and maybe D.C. is the only place he knows he can get a copy of the game. In that game is some combination of household substances that is a surefire zombie exterminator. Eugene knows that if he can run a copy of the game, get a list of materials, and collect them, he'd have a way to save the world.
Basically Eugene's logic is, "Of
course it will work. I mean, why wouldn't it?"
Remember, the guys in
The Return of the Living Dead treated the "stab in the head/destroy the brain" method as canon simply because it worked in
Night of the Living Dead. Right up until it didn't actually work.
I'm just throwing stuff out here, but this would seem to cover all the facts so far. His gaming references, his lack of competence in real life... also his self-importance and apparent sense of entitlement. He acts as though he really has something.
It's possible he really is a scientist who has access to a real cure, but given the tone of the show this seems unlikely.
It's also possible he's a bull artist who has nothing at all and who's scamming a free ride — but that also seems less likely. He doesn't have the necessary personal charm or social graces. And a stone-cold scammer who's willing to let people die for him doesn't seem like the type to go back for Glenn & co.
So, his arrogance is for a reason. He really thinks he's got something and can save the world. Of course it's "classified"; it bolsters his ego if he knows something that other people don't.
Poor guy.