MM,
In our experience, the college coaches had heard of or seen him play travel ball the previous summer (as a rising junior). So they were tracking him (and others in our area) and wanted to see how he was progressing on the mound as a junior. Our area is a hotbed for talent, so I know he wasn't the only local player they were tracking at the time. Typically, they would email him and ask him if he knew when he was pitching. When they showed up they typically had their school logos on their shirt or hat. There were a couple times when they came incognito. In all cases, these local coaches followed up with his high school coach about his character and work habits. Then they would follow up with my son with pitching feedback.
So, I was trading notes with a couple other posters who were telling me about some quid pro quo arrangements some of the college coaches and local travel coaches have. They'll do each other favors by watching / providing writen evaluations of a recruit they can't travel to. Personally, we never experienced that (to my knowledge) but I think this is going on now for programs that have to recruit across the country (ie...high academic schools) and can depend on some local travel coaches evaluations. This makes a lot of sense when programs are initially considering a recruit but don't have the reach or bandwidth to get there.
Good luck!