Yes, for any single one out of these 1.7 million to collide with one other the probability might be 0.5 (didn’t check it).
But he uses it in the sense that it is true for each of them, which it isn’t.
To stay with the birthday example:
If I enter a room with 22 of the unique people already in there, the chance that one of them has the same birthday as me is 22/365=0.06 and not 0.5.
Yes, for any single one out of these 1.7 million to collide with one other the probability might be 0.5 (didn’t check it).
But he uses it in the sense that it is true for each of them, which it isn’t.
To stay with the birthday example:
If I enter a room with 22 of the unique people already in there, the chance that one of them has the same birthday as me is 22/365=0.06 and not 0.5.