Obviously, the guy wasn't going over there for bible study with his new found friend. So what? He's an adult. He thought he was meeting another adult. Even if he went over there because she promised to let him dress up like the Big Bad Wolf while she put on a Little Red Riding Hood costume, there's nothing illegal about it.
There is absolutely nothing in the article that states or implies that he was intending to meet someone underage. So what if he met her on MySpace. It's also used a lot by adults. After those stories on Dateline about PervertedJustice doing the stings to catch child predators, my wife and I sat down at the computer together to check out Perverted Justice and MySpace. We were shocked to realize that within a 20 mile radius of our home, there are over 100 "adult women" (this story makes me wonder about that), who claim to be "just looking for fun". Some are married, some are single, some claim to be married swingers looking for other couples to have "fun" with. Big deal. If they are adults, then so what, to each his own. It may not be the kind of lifestyle that would endear them to the church activity committee, but it's not against the law.
Two weeks ago, I hopped in my truck to run to the store for some groceries. Guess what? I got out of my truck and was halfway across the store parking lot before I realized I didn't have my wallet. It was sitting on my dresser at home. People forget their wallets. It happens sometimes.
You sarcastically comment that he might have suspected he was walking into a robbery, which is why you suspect he intentionally "forgot" his wallet at home. Personally, if I thought I might get robbed by going someplace in particular, I wouldn't "forget" my wallet, I'd just stay away from that place. This sounds odd to you, I'm sure, since your logic train says forgetting the wallet but going anyways is suspect behavior. What would you do? Oh gee, I might get robbed if I go there. Well, I certainly wouldn't want the robber to be disappointed, so let me stop at the ATM on the way over and get plenty of cash. From your comments, this would be what you consider to be normal behavior.
All in all, I think your main objection with this guy is that he went over there, you beleive, looking for sex. Although that is probably a correct assumption, there is nothing in the article to verify that assumption, and even if there was, there isn't anything wrong with it, considering he thought he was meeting someone that was above the age of consent.
Based on the entire article, I think his story stinks.