These are two really good picks. Both prospects were good enough to go in the 1st round. The film on Ersery is outstanding.
As several people have mentioned, draft rankings can differ widely among teams. It can be a matter of need or a matter of subjective grading. If a team doesn't feel like it can get good value drafting at its spot, or can get better value by trading back, then it makes sense to trade. Instead of thinking of pre-draft player rankings as pure numerical order based on talent, it's more like successful tiers/buckets of talent and fit. If the texans didn't have a 1st round grade on anyone in the first round at 25 but had 20 or so people with mid-30's grades, it makes more sense to turn that 1 first round pick into two 2nd round picks and get two people. Also if the draft is shallow at the top but deep in quality players at an area of need then it isn't as necessary to use a first round pick there. There's a ton of starters (if not stars) that come out of 2nd and 3rd rounds.
So essentially they dealt 25 and 58 for 34 (Higgins), 48 (Ersery) and a 3rd next year. I like it! Hit the two biggest needs with guys who were solid value, and they added draft capital next year. Hope they both hit!