I suppose it kinda makes sense, Luke worked with Ross Emery (Block 2 DoP) on Alien: Covenant as well. I wasn't that impressed with the Last Supper short he directed or the two BR2049 prequel shorts either so don't know how he will fare here. Haven't seen Morgan either. Safe to say the series will probably take a bit of a dip in quality after the first two episodes with the second unit guys in charge now but it's ultimately the writing that will have to buoy-up the whole series.
I suspect TNT is trying to give the impression that Ridley Scott is directing the entire series since they have been absolutely mum on who the other directors will be. Their earlier press releases also gave the impression that it would all be directed by Riddles.