Their lottery is provably fair and the winners are determined randomly through some mathematical calculations.
Every time they announce the winners, you can easily download the tickets list from their twitter post and verify the winning lottery tickets, if you have some basic mathematics knowledge.
I wrote above that it is very easy to do so that a fake ID User wins the lottery. You just manually wind up 1 billion tickets for him, for example, or a 99,9% chance of winning. No one can determine this, you need to be the administrator of this site.