Colleges could certainly be tracking what you click on their web sites, or whether you view images in emails that they send to you. If you go to a college’s web site by clicking on an ad on some other web site, or by clicking on a link on social media, the college could be tracking the source of your click.
Any of the above could be used by the college to determine how effective its marketing is, and to estimate the likelihood of an applicant matriculating if admitted (“level of applicant’s interest”).