Well, I'm not familiar with the species that you're describing.
However, last summer a bunch of chinese elm seeds fell into a pot that I had outside after discarding the houseplant that had died in it.
I watered them just for the hell of it, and a week or two later had about 50 little sprouts that looked much like you describe your seedling. Over the summer they grew but it took about a month for them to be recognizable as a tree sprout.
I guess what I'm trying to say is, wait and see. It's probably your tree
