Saying the activity has to be interrupted is too narrow a requirement. It's more a question of something that was going on, in the background if you like, when an event occurred, in this case, your meeting. Now if you use simple past for both clauses, the suggestion is that you had several meetings, which were on the occasions of the multiple times you studied -- for example, you ran into him every time you had an English class.
As to your last two examples, they're essentially the same thing from a tense point of view, but with the clauses inverted and an alternative choice of words. They are fine, too, but not an answer to the original question.