McMillan Running Calculator

Many of us use the McMillan Running Calculator to determine race times based on other race times. Usually I find this tool pretty accurate however, after last Wednesday speed workout I'm not so sure what to think. 

Last Wednesday we did 5x1000m at 5k pace (the intervals are the circled splits). Pacer Joe paced us through the workout and said that each of the intervals were right around 7:00/mi pace.

Just for kicks, I entered my 1000m split time into the McMillan Running Calculator to see what the actual 5k pace was. 

Now, McMillan lists 5k as 5000m. This is where I get confused. when I entered 4:23 as a recent 1000m time, McMillan determined that is equivalent to a 8:18 5000m (see picture left).

Who's right? Pacer Joe or McMillan? I find it hard to believe that the Nike pacers would be off by that much. Am I using McMillan wrong?