Giventofly a date is like a meeting where you get to check each other out. There may be a 101 reasons why he, on second thoughts, didn't want to proceed: perhaps he didn't fancy you, felt there wasn't enough chemistry, didn't see you as potential girlfriend material, wanted a shag and didn't get one, is in touch with lots of girls, has got back with an ex, thought he was ready to date but isn't and so on.
I don't think anyone owes you anything after one date, and to seek a detailed explanation is just embarassing. I have also used internet dating, and if any of the guys I only dated once asked me I would have been mortified, you can't say 'well, you were too short and I didn't fancy you and you seemed a bit weird' or even 'I thought you were really attractive but I can't see us together'. I did once have a guy do this after a few dates, ringing up saying 'but why don't you want to be with me'. In the end I moved away and didn't let him know my new number- why should you have to justify why you don't want to be with someone.
This is why all pro-internet daters don't do long 'getting to know you' stuff beforehand, texting /emailing/phoning for weeks, because then if the first date you find there's no spark, too many expectations have been set up. First dates are just a screening process, not the main event.
The only sympathy I have is that he said he liked you, would like to meet up and so on. I have come to the conclusion that the occasion kind of demands this, so if he just said nothing on the date, it would be very difficult, so men often say they really like you as a way of keeping their options open/to cope with the difficulties of not being sure/to be polite. It's like saying 'you look lovely' when they might be thinking 'OMG'. The only true test is after the date, and you have all been polite and said 'let's meet up', to see if they call and make another date. I would not bother with anything less than action, words are cheap.