Does the rule for not needing particles on relative dates still apply here or do you need the は to emphasize that you're saying yesterday specifically was October third
I didn't put は in the sentence and it got marked wrong.
I'm guessing that in this specific sentence you need to emphasize that 'yesterday' is the topic of the sentence
There's no reason. The system can't easily determine where one word ends and another begins because Japanese doesn't use spaces. Often, the system splits words wrong, but at this point there's nothing we can do about it.