When is six miles really NOT six miles

Coming down I-93 south through Windham New Hampshire earlier, I noticed one of the "smart work zone" message boards for the widening work displaying "NO DELAYS TO EXIT 1" / "MASS S/L (means state line) 6 MILES".

But what really caught my attention was that this message board was placed right next to a permanent milepost indicating "South 93 MILE 4.8".

And of course, Murphy won again - this was the morning I left my camera at home.