Half of the websites when I google and sometimes the AI summary depending on how it’s googled. This became a debate with my wife last night. I said only iron is ferrous she said showed a bunch of references to Nickel and Cobalt as ferrous.

I also found this in Wikipedia, which seems the most likely reason for the terminology confusion:

In chemistry, the term is largely obsolete, but it often means iron, cobalt, and nickel, also called the iron triad;[1]. It may sometimes refer to other elements that resemble iron in some chemical aspects, such as the stable group 8 elements