A conflict of dates but......
I am aware of this source.
It is second hand information in a modeler's periodical. Considering the volume of first hand information and original documentation I have seen that contradicts many Barnes and Noble histories, you can put in stock in it if you wish.
I don't put much in it at all.
By the time any pilot got close enough to identify whether or not the target had an oil cooler on the chin, it would be way too late. I don't know how much experience you have actually flying but good luck spotting a feature like that on another aircraft outside of engagement ranges.
I highly doubt Hermann Graf did not realize this simple fact.
I would bet the author misinterpreted a valid order that had nothing in common with the meaning he gleaned from it.
More likely he read a recommendation originating from Zirkus Rosarius which probably went along the lines of "dogfighting is not altogether recommended".
All the best,
Crumpp