Based on the description, it appears to be a site-wide link, possibly originating from their above-the-fold or footer navigation. This is a standard practice for certain collaborations and something I would advocate for, but not solely for SEO purposes. Instead, the goal should be to drive genuine traffic rather than simply obtaining a large number of links (which, at that scale, are likely to have minimal value) from a single partnership.
In some instances, an excessive number of links from a single origin might be perceived as inauthentic linking practices, potentially resulting in a Google penalty. If you're concerned about the quantity of links from a single source, Google Search Console's Disavow Tool can be used to instruct Google to disregard those links.