What was happening ...?
Use the past continuous to express what was occurring at a precise moment in the past. The past continuous is often used together with the simple past to express an interrupted action. The action which was interrupted is expressed using the past continuous, while the action which caused the interruption takes the past simple.
Subject + to be + verb + ing + objectsThe Chicago branch of our restaurant business was struggling when Brando called.
Subject + to be + not + verb + ing + objectsI wasn't feeling hungry when the buffet opened.
Wh? + to be + subject + verb + ing?How were you working on your people skills when the trainer arrived?