> I can understand what they mean if they use "shill"

You kind of answered your own question. Many people never differentiate between bot and shill, instead preferring to lump those two words together. A bot is programmatic; a shill is a human agent that likes to amplify messages or spread disinformation manually. Although some shills may still use some level of automation, for example, often using several accounts at the same time using some bespoke software arrangement.