If everything is working perfectly, then sure. But maybe that cheap 30A generator isn't running well enough to trip its 30A breaker and it's trying its best to backfeed 20A of current into the grid. Or maybe the other 5 neighbors on his pole transformer tripped over to generator or solar, so that one guy is able to power his pole transformer while the lineman is trying to work on it, or maybe he can't figure out why the breaker keeps tripping, so he keeps resetting it, only to have it trip again a second later, meanwhile he's sending surges of current into the grid.

Utility workers will normally ground de-energized conductors before they work on them, but they need to do it perfectly each time to protect themselves from backfeeding.