It's different because you CAN get him at lower levels. It's very misleading.
You CANNOT get him at lower levels. But you CAN unlock him for lower levels. Big difference. You have to have at least one level 50 to get HK and he should come with all level 50 gear. When you unlock him for lower level toons tho, he still comes with the level 50 gear that has be changed out for level appropriate gear.
Best bet is to buy gear from him on GTN or use comms to buy him gear. It's worth it because I've used HK on my lower level alts and has all his level 50 abilities and is hard to kill. Plus he kills quicker than most other companions you acquire.