It’s because Dortmund played a whole different playstile under Klopp and later Tuchel what we play. I remember watching him at Dortmund and they always just killed the teams on the break and I expected to see more of that but he joined a Wenger side that has become so poor in transition so we couldn’t really string proper counter and Wenger didn’t like playing long balls. When Emery came in we improved a bit but only for a short period before becoming even worse and more passive. So Auba had to adapt to having the ball on the left against a defence in the low block.
He adapted perfectly. Haven’t been this confident in our player scoring before they even striked the ball since Van Persie. Auba is hitting his second prime at Arsenal and you love to see it.