How do you know if a "player" is a bot account?

This is pretty strange, I wrote down the username of an ally I thought was a bot, Looked them up, and the match I played with them does not show up in their match history. They would sit at base for 3-4 minutes at a time, dive in 1v5s, and go in brush to just sit there for minutes at a time. Their movements were just too similar to what I've seen bots do in custom games. They did not use chat to respond to allies, and the only time they would ping is when using TP (which bots do this as well). I was wondering how do you tell if an account is actually a bot account, and what does riot do about it once reported, or how do you properly report it? Thanks all!