It doesn't hurt to leave a bass in its case for a few hours upon receipt. I once had the lacquer on a bass crack because I'd been out walking in sub-freezing temperatures with my bass in a case and didn't wait before taking it out once I arrived home. In your case, maybe the inside of that delivery van was nice and warm - and maybe it wasn't. BTW, I've always been told that it's not so much temperature swings that are the problem but rapid changes in humidity levels. So even if your bass was in a warm environment prior to delivery, it very possibly was not in a sufficiently humid environment.
Edit: I just pulled up an email from Roger Sadowsky on the subject (I'd asked him the same question you are posing here). This was his response:
"The best thing to do regarding cold, is to let you instrument warm up
in the box/case for several hours before you open it.
Generally, humidity is the enemy (high or low), not temperature."