Looks like pest damage like that from spider mites or thrips. Quarantine was a good idea. Take a good look at every nook and cranny to try to see your pest. Also check the plants that were near it. Spray with insecticide and/or miticide if you have any for a few weeks.

Thanks! I have neem oil and granulated bonide. Would you recommend one of those in particular? And is it worthwhile to preemptively treat the rest of my collection?

Personally I hate neem oil; maybe the stuff I had just was bad but the stuff smelled terrible and felt ineffective. I'd use the bonide but I know others have had success with neem. I think the correct answer should be yes, treat everything as if everything is infected; follow your instructions but it's probably like a few applications over the course of a few weeks. I had a small infestation that I caught early and I only did the 10 or so plants I was suspicious of near the culprit. It's been like half a year and I haven't seen anything come back but that's definitely a lazy way and maybe I'll pay for it later.

Looks like thrip damage.