What did this fish smell like? Chinook (springs), particularly the Fall whites, have a very strong odour. I hate having to handle them as they leave a rather nasty scent on my hands, which I always wash off vigorously before touching my bait. Also, chinook will have distinct black gums (and mouth) which you already know.
Square tail would indicate a trout or steelhead. Both steelhead and chinook have spots covering both lobes of the tail. But the tail of a salmon will be more forked.
A picture would have been very helpful. But I appreciate that you released the fish unharmed instead of trying to get a photograph. Perhaps this will become an interesting memory for you - your mystery fish on the Vedder/Chilliwack.
Perhaps one day you will catch another, and put two and two together to figure out what species you released. This happened to me on the Squamish. In 2001 I was flyfishing for pinks and hooked and played a mystery fish. It was chrome, large, and gave me several knuckle busters from my fly reel. I had the fish laying on its side in the water when my leader broke. So the fish casually swam away before I could get a good look at it. I wasn't sure what it was, but years later I've come to conclude with 95% certainty that this was a chinook. I made this conclusion based on the run timing, the size of the fish (estimated 12 - 15 pounds), and how chinook fight on the end of a line.