He called me a "fiery ball of emotions", what?!?

My best guy friend of 3 years is my crush. He is dating someone right now, so we "just friends", or whatever that means. We still talk like we like each other so I just don't get it. Anyway, today we were on the phone for about 1 1/2 hrs. We were jokingly arguing about how I am lying to him about knowing about some funny secret. And he goes "you are lying you know the secret! I know you by now to know how your voice changes when you lie to me." And I go "Oh geez, please let this go already!" And he said "Fine. I don't know why you just wont admit you know the secret. Its not a big deal! But I guess things that aren't a big deal to me are with you. I have to be careful. You're a fiery ball of emotions!!!" What does that mean???