The term spontaneous in thermodynamics refers to processes that occur without changes to the system. That doesn’t really apply here. “Spontaneous” boiling otherwise makes sense in the context of superheated water that starts boiling at the slightest nudge. This might very well be what she meant. I’m not even trying to say he proved her wrong. I’m saying he added insightful information. His conversation skills could use some work but accusing him of anything beyond that is a reach in my opinion.