I'll provide a fuller quote from Iger to give it some context:
"Our parks people in Walt Disney World believe during the peak holiday season that we were able to accommodate about 3,000 more additional guests in the Magic Kingdom per day thanks to MyMagic+.
"One of the, I think, most attractive features and one that I think will have possibly the biggest benefit is the FastPass+, which is the ability to reserve 3 times on 3 attractions per day, either before you visited the park if you are a resort guest, or the day you enter the park if you are a same day or a single day ticket holder.
"What we are seeing there is substantially higher utilization of that product among our guests than we saw with the traditional FASTPASS."
When Iger's talking about Magic Kingdom capacity, it's in the context of FP+ vs. FP.
What we all understand is that as ride capacity is allocated increasingly to FP+, less is available through traditional lines.
POTC and HM cannot accommodate any more guests than it the past but, now, more are using FP+ since neither attraction had FP.
In Iger's mind, MK capacity is up.
Repeating myself, is it any wonder WDW is such a mess?