That's weird! I think one of the Esri developers fixed it secretly. It was definitely creating a funny artifact, but now it is fine and I can't replicate the issue of earlier. I'm using Chrome 80.0.3987.122.
it must be some very strange issue on my side. Another interesting phenomena is that the artifacts created are not kept at scale.
In this image I zoomed out from the original sketches.
And here I've zoomed back in
And looking at the map canvas in the DOM, you can see they are added as SVG paths.
Executing map.graphics.remove(map.graphics.graphics) from the console will remove the first graphic, but not the associated artifact.
Executing map.graphics.clear() will remove the graphics as well as the artifacts.
We are experiencing the same issue in versions 3.35 and 3.37 too using the same ESRI sample.
Most of the machines are not able to reproduce (working as expected).
The machine on which it reproduces is using the latest Chrome(92.0.4515.107).
Reproducible on EDGE too on the same machine.
Note: When changed the API version to 3.30, it works as expected.