can someone help me out with something I saw today,

while I was in a main city I was switching between different jobs and as you do this your hp obviously changes, as I was doing this an afk player was healing my missing hp, but it was as if it was automatically doing it because of my missing hp, can anyone explain how he was doing this when he was afk, I can only think that he was using a 3rd party programme like a bot or was it a type of macro ?