Mold Breaker only cancels/ignores abilities. It has nothing to do with items.
As for what happened I can only really think of one explanation other than hacking, glitches, bugs, messups etc.
If X is pawniard's speed and y is drilbur
then 1.5(X)<Y
That means that pawniard did not have enough speed invested into it to outspeed "Y" even with a choice scarf on