Maybe it's a corona virus thing. FedEx brought my DIY stuff the other day. I opened the door and he started backing up real quick. I asked if he wanted me to sign anything and he said no. Practically ran away.
The coronavirus has people freaking out I imagine.
FedEx (and I think USPS) doesn't have to have the customer sign for their packages right now due to the whole social distancing thing...
So if you were opening the door without a mask on, he was probably worried as he wasn't planning on doing any face to face contact with your package.