It depends on whether the “643 from those applying under the Early Decision program” include both ED 1 and 2, since the 326 students they mentioned were ED1 admissions.
An acceptance rate of 56% for ED1 means that there were 582 ED1 applicants and that would mean that there were only 61 ED2 applicants, which doesn’t seem reasonable.
Last year they had about 640 ED1 applications, and they only accepted 297, so accepting 326 from fewer than 500 applicants seems too high an acceptance rate, especially since they are still dealing with the over-enrollment of the class of 2022.
On the other hand, 326 is pretty low for all ED applications, so who knows? The announcement is pretty unclear. The numbers also seem strange, since there seem far fewer ED applicants to Middlebury than in previous years, while the drop in RD applicants seems much smaller.