They send fake (non-existing) actor ids for votes to obfuscate the identity of the real user. It is “compliant”, but completely against the spirit of a public social network.
There have been discussions about how to implement this before. But it has to be done in a way that is agreed by other threadiverse software. Unless they actually provide profiles for these fake actors there will be problems since some software will look up the profile info to cache it, even for likes…
Personally I’m of the opinion of a standard header to mark a favourite message as a private one and use a random ID that the originating instance can use to validate the message as genuine. But, this needs to be adopted properly by all.