Neighbor claims my lawnmower did damage to their cars

I just got home from a trip, was home for two hours and I mowed my lawn as I always do and have done for 4 years. Same direction, same way. While mowing, my neighbor called me over and saId "My side window on my truck is broken and I think it must be from your mower." I told him that I was sorry but I do not see how my mower could have done that. I told him to go and get quotes, contact his insurance and let his insurance handle it. I told him I was not liable. His wife came out scraming that her other car was also damaged and acted like a lunatic. Again, I apologized that that happened to their car but it did not come from my lawnmower. Today, I got a 1500 dollar claim from their insurance demanding payment. I am not paying it. I did not admit fault and they have no witness or video...and I honestly think it was from their teenage new driver in their gravel driveway.