1. counting to 7. a lot of times when people pull it, they just drag it unclaimed and forget to do any damage before the first TP move so it takes 0 dmg from physical or magic and then when it does a TP move people count that move so your "6th or 7th" will be off. Depending on which approach your LS takes, best bet is to just claim it with autoattack or a nuke so there's no flubbing the count.
2. triggerhappy DD like bojack said. Someone may have tried to maximize time hitting it as it was TP'n instead of waiting so that will skew that as well.
Personally, depending on your party setup, I think building up to be weak vs melee doing magic damage works better, then DD can just auto-attack and weaponskill like morons and not screw it up. A good rdm can do this in their sleep and you can pretty much kill it from the 5th or 6th TP instead of waiting.