I don't understand this mind-set. You put players on the practice squad because you think they have potential or they might eventually be needed. They are the best players you have at the time. If you feel like you've got a chance of acquiring a better player, why wouldn't you do it? It doesn't mean you don't like the player that you've got, only that you think someone else might be better.
Olumba still gets the chance on the practice squad to improve his craft and try to compete for a roster spot next year. For all we know, he might even be needed this season if this player doesn't work out or the depth is further depleted. All this means is Dallas at the moment thinks this player might offer more. (Of course, it could also mean that while we have Olumba "under contract," we like this player and would rather have both in some capacity than just one of them.)