As a reminder, ESR thinks that women shouldn't be allowed around software engineers because they're part of a complex conspiracy to file false rape claims against them (http://www.theregister.co.uk/2015/11/06/linus_torvalds_targe...).
I recognize that he's contributed value to the OSS community, but over the last decade or two I think he's done far more harm than good. A number of his beliefs and writings are extremely problematic, and turning a blind eye to it because of his contributions taints the OSS community.
Another example:
"In the U.S., blacks are 12% of the population but commit 50% of violent crimes; can anyone honestly think this is unconnected to the fact that they average 15 points of IQ lower than the general population? That stupid people are more violent is a fact independent of skin color." -Eric S. Raymond
That is ad-hominem. What is a person? His beliefs - and actions - of course.
Well, I imagine that you could argue a person is the structural disposition of a bunch of atoms, but it easier to summarize that as "beliefs".
Ad-hominem attack means diminishing some actions/qualities of a person because of other actions/qualities of said person, and that is what the parent was arguing. Not that it is always inappropriate, but it is ad-hominem.