For what it's worth, I think the term comes from giving metal a quick spray of primer immediately after shot blasting just to stop it rusting until the proper finish can be applied. The car wouldn't have been shot blasted or anything but it just means that the inside had been stripped and then had a quick blow over with primer. No need to do anything more. Main requirement is a for a good running engine, so they strip it down and perk it up a bit.