iPhoneX answered call by shaking or impact?

My iPhoneX recently answered a call seemingly from shaking or impact where I had gently tossed it onto a chair/cushion? It was laying next to my dog. I do not have it set for auto answer. I did not answer the phone. I did not even know a person had called, but found out later that they were on the line on my phone for several minutes waiting for me to get on the line. Any ideas? Would like to prevent this going forward.