Is this a warning sign when my boyfriend got mad? ?

We were playing tennis at the high school when a carload of guys drove by and whistled and hollered things at me. My boyfriend was so mad that he threw down his tennis racket and charged off toward their car like he was going to beat them up. I had to hold him back and then he wouldn't talk to me when we got in his truck. I've never seen him like that before, whats your opinion? Should I be wary or flattered?