The model was built by Bill George for fun and not originally intended to be a hospital ship, I think, hence the weapons.
Correct. I have some pics of the model somewhere before it was modified into the Pasteur. I believe it was labeled U.S.S. Olympic and the registry number might have been different. It was just a model George built in his spare time for himself. When they needed a model for the Pasteur, Peter Lauritson saw it and asked if they could use it. I believe that it was the only time a model built by a fan was used in a Star Trek show (well, except for Masao's space station in TOS-R.)