Where did you see that Sketch can be called by Metronome? If you were looking at the chart on Bulbapedia, a lot of the boxes under Gen 9 that are unchecked belong to signature moves, and even those that aren't don't seem to be callable be Metronome. I've been testing for hours, and while it is probable that I could've just missed it or misremembered, it'd be a pretty big coincidence that I didn't get any of the unchecked moves from Metronome.
In short, I don't think Sketch can be called from Metronome.