Hopefully they do a random lotto drawing for these since the assigned numbers are more first come first served looking. That would be the easiest thing to do obviously

That graph doesn't look like it was a single random number generator run. More like it was several runs done at different times.

Ex: 10,000 entries received by X date, 10,000 random numbers drawn between 1 and 10,000.
Another 10,000 entries received by Y date, another 10,000 random numbers drawn between 10,001 and 20,000

So, it has a degree of randomness, but the first batch of numbers generated all have lower numbers than the later batches of random numbers.

At least, that's what it looks like to me.

That's what I think it looks like.