The comment font appears a bit bolder because there isn't as much contrast between the rendered pixels, so your eye can't pick out the center line as distinctly as it can with your text sample from Google. You can see how this looks below, where the
t on the left is the "thin" one, and the one on the right is the "bold" one:
Based on the browser information you provided and the fact that I don't see this in 16.0.891.0, it looks like the change in the comment font is probably due to the updated version of Skia that was rolled into the 16.0.895.0 release.
I'm not familiar enough with the source code to know why there's a variation between the two sites, although I had thought it might be related to the slight difference in font colour and the relevance that makes in the code that was changed. Based on your comment that seems less likely now, but you could switch the font colour on Google to
#444444 and see if it changed anything.
In either case, it's definitely a result of upgrading Chrome. I actually remember experiencing this before for a bit before it went away, so presumably it'll go back again at some point (or at least I hope so).