I imagine the same kinds of people into car modding are also into modding other things. It probably isn't a huge overlap, but there are a lot of commonalities between the two. Additionally, a lot of Linux nerds also tend to be weebs and might have picked it up from Initial D or some other anime (never watched Initial D, but from the little I know about it, it'd make sense if the term appeared in it). The result is that it probably came from bleedover between the communities.