Here is the official tweet. Makes me wonder if the Martin signing was preventative knowing Warren might miss some time.
I would bet they signed Kelan independently, and because they like him. Essentially, you have a similar player in Sumner, Martin, and Jakarr, but you have them at different positions. Sumner can guard the 1 through some 3's, while Martin can guard 2's through 4's, and Sampson can guard some 3's through 5's. Tough nosed, engines always going, kind of players that look like they can hit a shot when need be.
Plus, I assume the Warren injury just popped up in the last couple days, or else Warren, Pritchard, all the players, and the coaching staff hid it well in all their interviews. Doubt it's been going on for 2-3 weeks, as Martin was locked up before Thanksgiving.