I only see artifacts around the man's hands - are there any other artifacts in the picture, or is there some sort of reason why the artifacts only seem to appear in that region?
One guess is the sudden change from the dark sleeves to his skin. If you look closely they appear all around his sweater too. As mentioned in the video you can apply bilinear filtering to smooth out the edges for those color as opposed to nearest neighbor.
Why do the artifacts gather around mostly some black region edges? Why not other places?
If you look at the background, there are artifacts there too, it's just that the artifacts are most noticeable with abrupt changes in color