Was that ever even a thing where a website could disallow linking to it?

There have been lawsuits about it! See, for example, https://www.seroundtable.com/linkage-lawsuit-15131.html (the first useful hit in a Google search for "lawsuit about linking"), and a survey article https://btlj.org/data/articles2015/vol16/16_3/16-berkeley-te... by Mark Sableman.