I’d get the boat and trailer id numbers and call ranger, see if they have any info. I guess I wouldn’t be too worried about the salvage title on the trailer if it doesn’t have any issues. Ranger makes one heck of a trailer. I suspect a bunch of fiberglass damage is enough to total a trailer, heck one idiot parked next to you could do that easy enough without structural damage.
Quite possible a (different) boat got totaled and they kept the trailer or something to that effect, or maybe that boat had some damage that was repaired and wasn’t enough to total the boat.
Either way Ranger might know something.