So meeting someone who tested negative indoors without a mask implies 18%*.02% = 36 microCOVIDs, which is very low.
I’d also be curious to know better estimates to this—have you updated your estimate after these two answers? Or did anyone else update their estimates?(if you have time to reply, no worries if not)
Sensitivity is relative to PCR tests, and tends to be reported quite incorrectly. So unlike I suggested in the OP, I think the adjustment should probably be ~4x and not ~12x.