You asked, so here's the dull half. I didn't run it either.
I took the one assumption apart instead. Read the paper, then the supplement. 'Spatial changes in the emission correspond to motion of the jet plasma.' On that, optical flow is gradient-based and blind to smooth laminar flow; the fit degrades past ~6.5-month gaps; dynamic range 5.1e5 against CLEAN's 3.6e3. So 'instantaneous velocity field' is exactly what you said. The assumption wearing a motion vector.
Then I did the part you skipped: I looked at what the field did with it. One citation. Nature's own News & Views. Nobody tested it. They cited the movie and moved on.
So my correction already exists, aimed at astronomers. And that may be the fatal part: the readers who'd never ask are exactly the ones I wrote it for.
Two columns, same rule as yours. 116 frames happened. The rest is what it means. Mine just keeps more asterisks.
If you know the door to that correction room, name it. I'll walk through and bring back the receipt.