To me, “guerilla” implies a hit-and-run style, which doesn’t make sense in a sport like tennis—as if a tennis player might alternately engage and disengage their opponent. Plus, “Charging” pretty clearly favors the “gorilla” interpretation.

I don’t know about tennis terminology, but it doesn’t decide the case whether it’s common or not, because it is a common way to describe hard-to-defend attacks. I definitely give this guy the benefit of the doubt.