Yup he's a cutie. I like the dumbo / big-ear bettas. He will grow. Even veil tail bettas get to be about the size and thickness of an adult thumb at full adult growth. Eh, I just about typed out a history on the different types but you can research that on your own so I don't type a novel LOL! It is quite interesting to learn about though, if you wish to. You can find out quite a lot by googling different search terms. :)
I can't tell if he is a king or not, but you might want to think about getting him a bigger tank eventually. (I'm not harping on you, just advising.) 2.5 gallons is pretty much the minimum recommended size tank, but a 5 gallon is ideal for bettas. I think a 10 gallon is minimum for kings but don't quote me on that I haven't researched them much because I don't have any.
1 gallon works but you will be doing crazy water changes and it's really quite small for them to swim around in as they get bigger. I do however love how you decorated your tank. :) Just wanted you to know he might be happier eventually in a bigger home.
Just wondering if you named him yet?