Day hikes up the MR (or anywhere else) do not require a bear cannister. Overnight hikes do. Did you tell them your trip was overnight? (They might assume otherwise.)
I think that map has been superceded.
Each time I've picked up an overnight permit in the Whitney Zone, either main trail or North Fork/MR, I had to initial a box indicating that I knew and agreed to bring and use a bear cannister. You can rent them at the visitor center for dollars a day. Also, most people leave it at their campsite with the rest of their overnight gear when they summit.
People also camp and use the smaller bear cannister, which is not much lighter, or no bear cannister at all. Rules are broken all the time.
