Chase could pull from all three credit bureaus. It may have to do with geographic location, or it may just look random, we don't know. Personally, Chase tends to double-pull TU and EX for me. They have never touched EQ.
Just another note: In the past, Chase/Southwest has offered a 50k sign-up bonus for the card. So the current 25k isn't nearly as appealing. Unless you really want it, perhaps consider holding out for another 50k promo.
