My neighbors propane grill caught on fire yesterday when not in use. is that possible?

I guess it would be possible but as asked by someone, what lit the fire? The propane could leak but something has to cause ignition. Sounds fishy to me. Now if they had been using it and there were some hot smoldering stuff inside it and the propane was leaking I guess it could catch. Quiet a few things would have to come together to make this happen.