why its unprofessional? lol.
uhm .. lets see..

first, they wrote the wrong name in the offer
when he noticed this, the reply was:
“you just accept this, later in contract we will change that name“

it wouldnt hurt if they actually checked WHO they are actually offering the the job to.

OP: please tell your friend to never sign something he is not sure of, that goes out for anyone :)