So, I started New Vegas today, and a little square pop-up said "New Content has been added". Then, proceeded to prompt me with the following 2 messages:

"Yes, restart the game."

or

"No, keep playing."

What was this about? Was it because I have DLC? I don't really understand.

I asked one of my friends if it happened to him, but I forgot he has no DLC. So, i'm guessing it was DLC-related.

I really dont understand what you mean?