an expression of time can be used as an interruption as well
we were eating dinner at 4 o'clock.
at 6 o'clock we were still studying for our test.
here are some more uses of the past continuous parallel actions
past continuous is used to show two actions happening the some time the past ,like in these examples :
i was reading and he was watching TV.
while she was sleeping ,jack was doing his homework.
notice the word "while" is often used in these situations :while i was cleaning ,she was watching television .
he was talking while she was studying