Sounds like the first time I roasted on a whirly pop. Your temp was definitely way too high, no need to get a thermometer to verify. You could not have had so many beans enter first crack in two unless it was true. Does seem to suggest uneven mixing though, clearly some spent more time in contact with the drum than others. Unless you turned off all heat and the beams initially in contact charred and cracked, moments later cooling the drum dramatically but leaving the first beams to drop close enough that after turning back on heat they weee able to finish quickly?
Yes, i you per this on an iPhone