I think it can be a sign of HD, in so far as that sitting properly causes pain and sitting to the side is a way to ease the pain...but I don't think that just because your dog sits to the side it's means he has HD. My dogs sit to the side when they're feeling relaxed, especially the puppy becaused she's all floppy limbs anyway.
The safest thing to do is just go ahead and get Xrays. We do Xrays at 6 months just to make sure nothing is radically wrong before we start working the dog. OFA won't certify hips until the dog is 2, but many people get prelims done before then and Germany will certify hips when the dog is a year...so you can defnitely do Xrays now and go back to Xray again at 2, which will give you peace of mind.
The safest thing to do is just go ahead and get Xrays. We do Xrays at 6 months just to make sure nothing is radically wrong before we start working the dog. OFA won't certify hips until the dog is 2, but many people get prelims done before then and Germany will certify hips when the dog is a year...so you can defnitely do Xrays now and go back to Xray again at 2, which will give you peace of mind.