Schmoe was being judged with zero empathy right now, for the record. This was clearly a waste of time when she could actually be studying something useful and whatever he had clumsily tried to turn her answer into was evidence of that.
As for an assumption....... Pax just went with one that was essentially true, because why not? She didn't feel bad about it, for reasons she had just expressed, and also because she wasn't taking this seriously at all.
Pax added it to the pile and returned to her seat. If this lesson didn't go somewhere soon...