I can understand the DCT not wanting to go that low with high rpms if the car was still being broken in. But did you try multiple times? As crazy as it seems it may have been humor error. You may have not put it to 3rd when you downshifted so fast.
Not to start a war but I didn't like on my 335iS how the dct did not shift all the way when I would downshift very fast. I opted for the manual because of this.
MY13 Black / Black 991 911 7mt
MY15 F80 BSM/Full SO DCT