There seems to be something wrong with the images. I see the difference in Chrome too, but Photoshop CS 2019 reports that there is an issue with the embedded profile and discards them. In addition, they apear to be in color mode: B&W with a color icc profile, something that is not allowed, at least in recent versions of photoshop.
Extracting the ICC profile with exiftool, changing the color mode to RGB and assigning the profile in photoshop shows the image correctly, so I would say it is not Chrome to blame in this instance.
Hmm, the image represented grayscale data, was recognized as Gray by PS CS5 at the time (this was a couple of years ago) and as I recall was then assigned a 'Gray Gamma 1.0' ICC profile. The profile was created and assigned in PS CS5 by modifying the built-in Gray Gamma 2.2 profile to linear. I believe this is all standard stuff so it should work, and in fact it does work (some of the time)*.
However obviously things have progressed since then because I see that CC2019 now complains when opening the relative file. When the image is downloaded from the web page and opened in CC 2019, PS still recognizes it as Gray but marks it as untagged, saying that the ICC profile is invalid. Plus, while the image still appears dark on the web page viewed via Chrome, if I point Chrome directly to the downloaded file it shows it at the correct brightness. Weird, let's assume it is a 'old' profile issue.
I'll replace the old image in the article with the same with a Gray Gamma 1.0 profile assigned in CC2019, that should do it (for now:-). Let me know if it fixes it for y'all.
[Edit: I see in fact that it does not fix it, at least via Chrome on my 3 Win 10 computers and two Android phones. On the other hand now CC2019 no longer complains when opening it - back to the Color Management drawing board, Chrome. BTW, Photos hangs on either version, while File Explorer W10 displays the old file correctly but not the new ones. This CM stuff is a hoot!].
Thanks for the feedback, learn something new every day
Jack
*Incidentally, for those of us that don't do this every day, when PS opens an untagged image it tries to figure out its type (RGB, CMYK, Gray, etc.) and displays it as is. It's up to you to then tell it how to deal with its tones by assigning a suitable profile.