I guess he meant the microSD card slot.
But its a bit confusing for me aswell.
He means Micro USB, the Amlogic C76 A113D has no Sd/Tf card slot, only a Micro USB, regardless, as Phill mentioned above, the k version is not supported by BraiinOS yet.
I also have a paranoia over the letter K in any Antminer Bitmain makes, this letter brings back sad memory of the S9k, I think k stands for KABOOM!, Bitmain collects all the bad chips and stick them on all the bad control boards they have and ship them to us like hot potatoes.