Yeah, it could be contextual but here it would just stand to mean that he prevented her from being put in that uneasy situation. The tender guy that he must have been.

It appears the meaning of the word in this sentence is intended to mean “interrupted “. So, “She was just about to apologize when he interrupted her”. The word preempt as a transitive verb means to take place or prevent something from happening or someone from doing something . So yes, in a sense it depends on the context but also , or perhaps more heavily, upon the direct object that follows.