Nah. The guilt by association fallacy is more like:

• [P1] Hitler ate bread.
• [P2] Hitler was a bad person.
• [C] Thus if you eat bread, you’re as bad as Hitler.

That is not even remotely close to what the DinoCon is doing. If we interpret their actions as an argument, it’s more like:

• [P1] Knowingly associating yourself with a bad person makes you a bad person.
• [P2] Those people knowingly associating themselves with Epstein, a bad person.
• [C] Thus those people are bad people.

You might disagree with the first premise (it’s a moral premise, so it depends on your values), but the argument is perfectly logical.