I think kids are looking to see how the fit at schools and this is why schools do these overnight visits. The kids can actually “see” what life will be like there. Since your son had a fun visit, he now envisions himself at that school. He now has a vision of what college is like, and it looks like what he experienced on his visit. It might be a challenge to get him to change his perspective.
I think your plan to revisit the school you prefer is a good one. Do some research beforehand to see if they have gaming clubs, etc. your son can get involved with and point those things out to him when you are there. Time your visit carefully for when kids are around. Weather has a big impact and you can’t control that but so does the time of day. You mentioned 5pm Friday. Depending on the time of year that might actually be a quiet time. When the weather is nice a lot of kids would be out at that time though at my D’s school but she is often at the Library at that time so she can go out later. Can your son attend a class on his visit? Can he eat lunch in the dorms? Basically, what can you do to get him around students and see what student life is like there?
Good luck!