Who knows? It could be a million of reasons and you'll drive yourself crazy trying to figure it out. The reason you want to figure it out is because you wonder if it's something you did or said because if you could figure out what you did then maybe next time it won't happen. But the truth is that it could have had nothing to do with you or what you did, said, etc. It could be him and his life or that he figured out he's not ready for a relationship, and the list goes on....ad nasuem...
You'd be better off just looking at it like when one door closes, another opens and he's just not the one, however, you got some experience in dating, pr whatever which was valuable and let it go....
You said you weren't clingy because he started all the conversations and that's not how I would define clingy plus it could have been a problem. Guys tend to get bored with women who don't have lives of their own, therefore they have something to contribute to the relationship. They don't want to have to do all the work.....you may want to think about that....and how you might find a balance. Instead of being a dominate of conversation or miss silent until spoken to, try to enrich your life and experiences so you can be a good conversationalist. Maybe he's a thinker and he wanted someone who could engage him in worthy topics.
Point is, you'll never know for sure unless you want to call him and ask and he's honest enough to answer you. I have wondered when guys acted the same way with me and many times they said they just didn't feel any chemistry between us although I was pretty, sexy, witty, whatever enough. You can't argue or change some things. Some people are just not going to fit you or vice versa.
It could be another woman he met, you didn't seem to be in a committed serious relationship, so he didn't feel he needed to call and tell you what happened. Some guys are too chicken to tell you directly anyway or they don't want to hurt your feelings, or they didn't think it was all that serious to go there and explain.....again, who knows.
I'd work on trying to change my way of lookinf at it....instead of feeling dumped I'd feel happy that the wrong one walked away because now the right one can come in. If you know that you were caring, considerate, a good date, then work on feeling more self confident because that's something that guys can sense about a woman. Confidence is a very big turn on to most men and it shows in the way you walk, conduct yourself, all kinds of ways.....
It's generally a waste of time trying to figure those things out, unless there's honestly something you need to change for future relationships. It won't be a waste of time to pull yourself up by your bootstraps and getting busy with making your life what you want.