It's hard to tell, since they don't show you the actual damage rolls.
It's possible that you rolled two 1s in a row for your weapon damage.... or it's possible that it rolled all of the damage twice, and this complete set was higher, but it also contained a 1 in the base weapon damage roll.
We can't tell, unfortunately.
We can't even tell whether it rolls the whole lot, adds them up, and then rolls them all again and adds those, or whether it's doing each die independently, or anything in between... I'd recommend reporting with with the screen shot to their bug form and seeing if you get an explanation of how it works in the response.