I was once asked what drugs I had taken, which confused me because I had taken none. A mirror inspection revealed that my pupils were hella dialated, for no apparent reason.
"On command" seems a plausible stretch from "spontaneously for no reason."
There are several reasons why you might have involuntarily diluted pupils, e.g. arousal, i.e. triggering a entirely natural response to a stimulus, even if it the stimulus is aehm "imaginary"/a thought (thinking about the sun).
This is called indirect control in the posted article.
Having voluntary control over your pupils is something entirely different, and just because you have dilated your pupils "by accident" doesn't mean your short of controlling them.
"On command" seems a plausible stretch from "spontaneously for no reason."