Ex threatening to sue me over money he paid for our shared meals

Location: California

I (M, 31) and he (M, 30) dated for 3 months before I told him we weren’t a match and I didn’t want to pursue this relationship anymore. Then he brought up the money he paid for my portions on the meals we had together during our dates. I refused to pay the amount he demanded and I offered only $100 to close this off. He’s still not happy and threatened to sue me over it. The approx amount should be about or lower than $400. He never asked me to pay him back and even texted me to demand that money until I texted him I wanted to end this relationship.

Is it possible that I might be served? What should I concern about this? Any advice would be appreciated, thank you.