I don't know... that seems a bit of a stretch. By this argument you could say any break&run in a competitive match is a drill. Regardless of difficulty....
If 'I' had to define a drill. I would say any repeditive activity that involved predetermined ball locations.
Breaking = drill
Dealing with a random scattering of balls after a break, (ghost or not) = not drill.
Most of the time at home I just throw 9 balls out on the table and shoot, essentially ghost ball but I don't break. I consider that a drill in my opinion. I have two drills I use whenever I do drills but they get boring and in reality, I'm at a stage where my pocketing abilities really should result in more B&R's but for whatever reason they don't. So, by throwing those balls on the table and just trying to run through them I am, in fact, working on weakest part of my game - running racks. Consistency comes with sound fundamentals and repetition. My fundamentals aren't perfect by a long stretch so I will work on the mighty X drill and another random 15 ball drill to work on rebounds (rail action depending on how far the OB is from the rail) and angle of departure (in relation to the table I'm shooting on. i.e. if I'm cutting a ball on the rail and hitting it at 45deg can I draw the CB back out of there at 60deg or only 30deg, those are the things that help me when in a game) when shooting balls on the rail, then, I'll go right back to trying to run racks.
Someone said drills can have diminishing returns and I think they were spot on. Yes, if I find an issue I will work on it a bit but, in general, I'm not going to sit there for hours practicing a particular shot and would rather work on patterns and shoot balls

In short - a drill is what you make of it
