I'm actually having a similar issue right now. I suspect it's using my username, instead of my Twitter name.
I have my company's Twitter name (without the @) listed, and it's using "@Dan" on our Twitter cards, instead of the company's Twitter handle. I am the author of every page/post, so that's why my profile has the company handle, instead of my own.
I am going to do some testing, but if you have any ideas, they are welcomed. If I find a solution or what lead to the issue, I'll be sure to post it here.
Edit: Apparently our server was having a caching issue, and WordPress was not able to properly clear the database cache via W3 Total Cache's flush button. Everything appears as expected now.