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That is not so much an assumption as a conclusion, backed up by research:

https://urban.uw.edu/news/crows-hold-grudges-against-individ...

https://crowlingo.org/journal/marzluff-mask-experiments-expl...

I think the person meant that it might not be for the mask-wearer. They might be targeted by crows even when the mask comes off because the crows might still recognize them from their walking style or body odor or voice etc.

They explicitly are not able to recognize once the mask comes off. That’s the point.

That's why you use your friend!

Or even better: use a (visiting) tourist.

Mostly face - at least crows. There were experiments done with people in mask, and when they remove the mask - crows would no longer recognize them