Sounds like that fish you had on might have been foul hooked which would have prevented you from turning it! Often when a salmon puts up an extra tough or unusual sort of fight the hook is buried some place other than it’s mouth. Sideways they are next to impossible to land. On the other hand it might have just been a very big strong salmon and the hook was only just holding anyway. We’ll never know which! It is a strange feature of salmon fishing that some blokes hook and loose quite a few fish each season whilst others land nearly every salmon they occasional manage to hook.