Ephemeral as in one-off. One of Alice, Bob or Carol liked and replied and we don't know if it was the same user or two out of these three. The account has no profile but provided proof to be from that group.
Discussion
The event would be standard nostr with a tag most clients wouldn't know how to interpret. Your client wouldn't find an avatar or username.
Awesome! Thanks! Will look into it. nostr:nprofile1qqst3axzay8sm4n8zg2n84acmt7hwwztpdg9r7p89e2f83v007f7zjcpp4mhxue69uhkummn9ekx7mqpy9mhxue69uhkummnw3ez6un9d3shjtnnvd5xu6t50fjkctnhdaexceq0axw5w has probably worked on something to enable this