How can he create this kind of backlinks without problems

So i was looking at competition backlinks (website a) and i noticed that there was this page (website b) that was creating alot of backlinks for this other website, and i found out that website b had a category that was just a link to website a so everytime website b posts something website a gets a backlink is this legit? How can both website do this without problems, it has been doing it since 2016