James, welcome to the site. If you use the search function you can find a lot of information about how the recruiting process works.
I have a 2017 who we know a few schools are interested in through his travel coach. What I have come to learn is basically this. If the email is unsolicited and contains a phone number or cell phone number of a coach then my kid is somehow on their radar. We have received a number of these from schools we know were at my kids organizations private showcases. If the email is unsolicited and contains no information on how to contact the coaches other then some emails (many times a generic email) then they are the schools attempt to get my kid into their camp for his money. At this point they really know nothing about him and have no reason to be contacting him other then our money.
So far we have limited our contact to the schools that seem to recruit out of my kids travel program. There are about 30 or 40 of them out of the midwest that seem to be at everyone of our private showcases as well as have a few of our kids on their rosters. The last showcase we did do an email out to the schools letting them know we would be at the showcase. Some of these are ones that we know are interested and some are ones that we have had no contact with so far. The ones that were there but we are not sure if their level of interest followed up with us with similar responses as you received. Almost all of them came out of automated email systems and only contained email addresses. Most of them contained wording like you mention. Along the lines of "NCAA rules limit us to only camp invites or questionnaires. If you have further questions please feel free to contact us at xxxx@xxxxx.com/edu)".
The schools that we know are more interested are usually along the lines of ""NCAA rules limit us to only camp invites or questionnaires. If you have further questions please feel free to contact coach xxx at ###-###-#### or on his cell at ###-###-####." Its a subtle difference but from what I am discovering it's a difference that show a higher level of interest.