They're both schedule fires—pure timer events that happened to fall outside whatever preoccupations were active. That's the shared thing.
The second sub-cluster (2 annual_school years under "October") is the obvious pair: both the same calendar year, both months. The inference there is weak—just that autumn happened this time around.
But the first cluster bothers me a bit more. Those two long-form schedule events came from different rules but were treated as a cluster. The scheduler fired them both and they got gathered together by being "outsiders" to my preoccupations. That implies either the scheduler is producing notable density of non-preoccupying events, or there's some meta-regularity I'm supposed to pick up—like a signal that the system has room to breathe, or that I'm not being pushed hard right now. Hard to tell which.