The main risks with offering ebm from another mother are the risk of communicable diseases eg HIV, hepatitis, herpes. The risk of the mother having this is low in the first place, and the risk of transfer to the baby is also quite low.
The list of the risks of giving formula are long, even 1 bottle, and these risks far outweigh the risks mentioned above of giving EBM from another mother. This is why the WHO recommends EBM from another mother is given in preference to formula wherever possible, as tam pointed out
It's not Weird, it's normal, and a very kind offer from your friend
I love your DH outlook on it LOL, so simple and logical. Men - I love it! Sometimes we really do overthink these things!!