Your repo keeps every like, repost, reply and quote with a timestamp. This reads all of it and, for every account you've crossed paths with, shows the first post of theirs you engaged with and the first post of theirs you liked, oldest first, with the words that were in them. When a first happened on today's date in an earlier year, it says so.
A repo records only what you acted on, so "saw" means the first like, repost, reply or quote. Public reads only, nothing written.