当時私は母が入れ物に入れた餌を自分で動物たちに与えた

I would have expected the above sentence to use てい form (与えていた) as it seems like a repeated action in the past.

I'm assuming the reason 与えた is used instead is the word 当時 (at that time). Is this correct? Are there any another common adverbs of time I should watch out for?