Volvo XC60 steering lock mystery

Car in shop w/ locked steering wheel issue. They advise replacing steering rack & pinion for $5K (!!). Dying to know what caused this & if replacement is truly needed. Leading up to the lock up, no trouble steering or noises or warnings about fluid or battery, and it wasn’t below freezing the night before. The night prior the driver turned the steering wheel hard right while parking and pulled front tire slightly up on curb. Next morn, I could move car back/forwards off the curb, but steering column had very little play & had pwr steering fail warning. Had it towed. I’m reading causes can be: salt can corrode, seal damage or dirty/low pwr steering fluid, u joint (check & lube), collision (no) or pothole (yes). Any other thoughts on causes or advice on what to ask the mechanic before paying $5K. (Rack & pinion can cost 2600-4600 per Google)