My guess would be they accept their target number at first, but then offer acceptances to people on the waitlist as other individuals decline offers. And the large number of admissions offers is a total that includes the offers that were given, even to those who were waitlisted originally.
So if that is true, you can almost guess how many people were offered admissions off the waitlist by subtracting the target enrollment from the admissions offers.
However, if there is one thing I have learned there is so much that goes into considerations it is difficult to predict how things work in the admissions world.