I assume they're referring to people recalling what Trump said, and that is hearsay. Albeit, I think it kind of became an awkward debate point mostly tossed around by people that heard someone say "hearsay bad!" and sort of ran with it. I mean... when I discuss the whole matter with people down here, I usually hear "it's all hearsay" brought up at least once in each conversation. LegalEagle has a video just on the topic of hearsay, which includes what's actually hearsay (spoiler: just about everything apart from the person actually admitting it) and when is hearsay typically admitted into court.
People recalling what they heard Trump say is not hearsay. It's just literally not by the federal rules of evidence.