The key elements I noticed were that the "wave" displayed a prismatic rainbow-style set of colors, the presentation of this prismatic color was stable (didn't waver or show shifts among the colors), and it exhibited smooth continuous movement from Sid's hand toward / unto the pot the woman was holding.
Based on these elements I zeroed in on a favored hypothesis early on, and I've been querying Sid in relation to refining this hypothesis ever since.
I may as well toss this hypothesis into the ring ...
If there's a mundane explanation, it most probably involves a transient projection of prismatically-colored light into the scene. This projected rainbow light was discrete and stable in content, and it moved quickly but smoothly for a short time before disappearing.
Given the relative locations and orientations Sid illustrated in his latest sketch, the most likely natural light source was in front of him toward his left - in the direction of the door and what I assume was the shop's windowed front.
In the naturally-lit version, the light source was a glint or reflection from or off a moving object - e.g., a vehicle passing by outside the shop. This glint (whatever) was refracted to give the stable rainbow colors - maybe by a window / door glass, maybe via something within the shop. The movement of the original light source and the path along which it refracted / reflected (i.e., optically ricocheted) into / within the shop made it a discrete projected image that moved a short distance in a short time.
This passing projection of a rainbow chunk happened to become visible from Sid's vantage point such that it appeared first at his hand's position in his field of view, and its movement gave the appearance of the colorful "wave" emanating and progressively extending from his hand.
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