DIFFERENCE BETWEEN SIMPLE PAST AND PAST CONTINUOUS:
If a new action happened in the middle of another action, you need both tenses: Past Simple indicates the new action (or the shortest action) and Past Continuous for the action already in progress (the longest action):

SIMPLE PAST | PAST CONTINUOUS
New action: The phone rang... | Action already in progress: ...while we were having lunch.

But what happens if there is only one verb? Do you just want to mention that an action took place in the past? Or do you want to put emphasis on the progress, e.g. that an action was taking place at a certain time?

SIMPLE PAST | PAST CONTINUOUS
Just mentioning : I uploaded a video | Emphasizing progress: I was uploading a video yesterday at 17:00 .

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