It's a reference to TFA :)

from your very link:

> ad hominem, type of argument or attack that appeals to prejudice or feelings or irrelevantly impugns another person’s character instead of addressing the facts or claims made by the latter.

> Ad hominem arguments are often taught to be a type of fallacy, an erroneous form of argumentation, although this is not necessarily the case. A number of scholars have noted that questioning a person’s character is a fallacy only insofar as the person’s character is not logically relevant to the debate.

You are right! The link does discuss cases where it's not a fallacy - in those cases, it is instead a valid argument. Again, not what you said.