Ask for time to consider.
Do your homework on the program and the school. Visit in person.
And do the same with other schools of interest, perhaps closer to home.
If being closer to home is what matters to your son, then this is not the right fit for him.
If you stick with the process, he may well land another offer of similar magnitude from a program he prefers.
But, if he continues to look into things, he may well find that he likes this place enough to travel further from home than he expected when he first started the process. So don't toss that offer in the waste bin just yet.
There is a lot to be said for going somewhere where they have shown you are wanted. And one thing about the partial scholarships of college baseball, you can tell who wants you the most according to which ones put their money where their mouths are.
The one thing I can tell from your post is, your son is not ready to commit just yet. But the offer may not be there forever, so he needs to get busy on doing his homework.