Ad hom is in a Venn diagram here, because the two are often used together but are not the same. An ad hom is specifically when you say something that boils down to "You're a scoundrel [or otherwise undesirable], so your argument is incorrect". The labeling strategy that Awoo is discussing is closer to equivocation (insinuating things are the same that are different) as a means of obfuscation, such as the "terrorist" example. See how so many people complaining about the Hot Houthi Winter interview with Hasan were calling the interviewee a "terrorist" in order to get people to not actually think about what he is, which is decidedly not a terrorist. What specifically the dude is saying or even the truth of it hasn't even come into play yet.
So I spent a minute there trying really hard to figure out the difference as I typed because it's honestly a good question on your part, and I think the answer is that this thought-terminating cliche bit is used to conclude that the person is a scoundrel, while ad homs are predicated on the person being seen as a scoundrel to falsely prove some other point (Biden being an imperialist does not make the time of day change when he comments that it's morning). The reason these are so hard to pin down, aside from the fact that they are informal fallacies, is that common communication and even argumentation is filled with implied premises, inferences, and conclusions, so mapping them out formally enough to be able to compare the structure is a genuinely difficult task.
What do you think, @Awoo@hexbear.net?
The thing is, if we believe we are on the side of reason, the nature of such an argument should only be considered a nuisance to us rather than catastrophic. If I want to prove that Israel is fascist and someone hits me with the "not everyone you disagree with is a fascist" line, then I can simply ask them to give me a set of criteria and either argue the criteria being incorrect or argue that Israel meets it (depending on the criteria, context, etc.) What our comrade is proposing is a way of opening discussion so that preconceived notions can be challenged more thoroughly.
Socialism is the ruthless criticism of all that exists; if a socialist can't produce a justification for their ideology, this isn't an argument they should be getting into (they should be studying, whether through reading or investigating the world).