Alternator problem: did the dealer do it?

I took my 2002 Grand Cherokee to the dealer for a recall to fix a potential air bag problem. I picked up the car and when I started it up to drive home the check gauge light came on. I saw that my amp gauge was very low. I turned off the car and tried to turn it back on and it was dead. The dealer said it was a bad alternator and it was a coincidence that it died seconds after leaving the shop.

What do you think? What are my options?

Thanks,