How should I reply to this?

theres a guy in work im friendly with (have a crush on, we flirt) he has a girlfriend which is fine, nothing more than harmless flirting. I was chatting to him and two other colleagues started whispering (i didnt see them) later that day though the guy i liked txt me saying i noticed say Daniel and Zara gossiping about us haha Should I reply? I should say something like thats ridiculous you cant chat to the opposite sex without ppl thinking there is something more going on, I dont fancy you..that kinda thing? I make out that I dont like him haha Its all a bit complicated. Why do you think he told me this ? It must have been on his mind haha Oh im a girl reading to much into it.