Good job by your son. I'm not aware of any move to make lacrosse Div. III. The CGA has lots of club sports but that doesn't mean they are not competitive and exciting to watch. The rugby club won a national title and the ice hockey team also plays club but goes against really good teams. The lax team plays schools like UConn, Boston College, Northeastern, BU and New Hampshire. As with many sports the CGA, which has about 1000 students, goes head to head with much bigger schools. Another example is crew in which my son's team beat North Carolina out in the national championships for fifth place.
A lot of it has to do with Title IX issues...some sports are called "club" even though they are in effect varsity.
The ice hockey team competes against schools such as UConn, Bates, Vermont, and Springfield. Again it is club level.
As far as KP their lax is D-3; but if you look at the schedule it is not overly impressive...Vassar, Mt. St. Vincent, Stockton...anyway again it probably is a Title XIX thing. They have very few women at the school so they can have different sports be varsity-level.
Anyway, good luck to your son in whatever he decides to do.