There are different types of Feeders both on the astral & spiritual planes. They are not brought on by any specific event; they are roaming entities that feed from hosts who are typically animals or humans. They are not beings that can be bound as spirits are bound, nor would you want to, as a contained Feeder is a dangerous situation for anyone in the dwelling/location.
To encounter one is somewhat rare, they aren't plentiful but it happens and being a Spirit Keeper or practicing in magic doesn't make you any more or less susceptible to being chosen as a host.
They prey on people who they think they can gorge on energy from. They start slow, they sort of pick at your energy, drain you a little and as your energy becomes more drained they do things to try and provoke more energy from you like fear, stress, anxiety, etc. They are highly evolved beings that can shape-shift not only themselves but also extension of their core energy to be multiple things which is what happened here.
In my professional opinion I think the monsters under the bed and in the closet are often Feeders because children are easily provoked and have a lot of energy. Feeders typically stay with a host anywhere from a few days to a few weeks before they move on. They don't stay in one place for long or with one host for long and they don't typically move from family member to family member. They roam constantly and feed from multiple sources because each of our energy is different and they do best feeding from variety and not from one energy imprint.