My guess is YOU stopped paying attention b/c xfiles was no longer cool...
I suspect that his passion on the issue was inspired by an experience. I have known a couple of people who saw things that defy explanation and you pretty much can't make them shut up about it.
I'm not screaming ERRMUHGERD ALIENS! I'm just saying that many people see things that defy the mundane explanations of passenger aircraft, birds, swamp gas and the planet Venus. It's perfectly normal for someone who has had such an experience to be interested in the subject matter.
To quote Donald Rumsfeld, "Absence of evidence is not evidence of absence".
I consider myself to be an open-minded skeptic.
I'm in the "Hey Stan, did you find that proof yet? No. OK. I'll be over here, let me know if you find it" camp.
And by all accounts considering that the amount of people with cameras increased by at least a ten fold since the 90's we should've the same an increase in UFO sightings as well, which well unless you count the text to speech youtube flicks about planet X and the anunaki didn't really happen.