This is a huge number of users for such a sphere, in my opinion. Due to the fact that until the end of the distribution is not enough time, I think these numbers will increase.
It's not a huge number ! if you are going to giveaway 1M dollar of bitcoin, you expect millions of customers specially when referral doesn't need to deposit money or make a trade to count. We are talking here about 1M dollar.
I just guess that they will get enough user but what if both user have same number of referrals as for the first place? Although it's just a very less chance of it tho.
Unlikely to happen, but they could pick up the one with more quality referrals or split the prize between the two winners.
I think it will be more fair if the team divides the prize between the two winners. Of course, provided that both of them will have quality referrals.