This is all taken care of by Rally up. I'm sure it's some sort of computerized random selection.
I'll get on my soap box now... We used this online method last year and I believe we almost made 40k for our local Hospice. It works well, is painless and helps generate money for worthy causes. In our little gun world I still see others trying to use tickets sold at shows etc. In my view this is the equivalent of carving a stock with a sharp rock. In a number of cases we've forwarded all the necessary information and instructions to others so they could potentially use this same process and they've chosen not to. If not using an online platform, you'll probably only make 1/3 of what you would otherwise, but many are so set in their ways and so distrustful they let this money lay on the table...
Frustrating to see...
Jim