The starter and the drive are always in contact, its the starter clutch that separates them. That and Neutral separates them, the later from the gear train, rolling the bike backwards while in gear is not advised even while the clutch is pulled, the clutch does not disengage this always in contact scenario that is one way. I believe that is the case because the starter is on the primary drive gear that is on the other side of the drive clutch. So even if the bike has its clutch pulled the contact to the starter gear is still there.

So starting the bike and then putting it in gear and with the clutch pulled and then rolling backwards is putting the area of contact in a direction it is not supposed to go…backwards and if the starter clutch is not fully retracted it could have caused the problem, it may have caused the issue.