It's actually really cherry-picked samples. All messages (blue and green) in the Messages app fade out slightly as you scroll. The author picked a blue message from the bottom of the screen and a green one from the top. If only they scrolled around a bit... they would have noticed.

Great point. I just now confirmed that as well. The bottom message is much darker than the one on top

Also the article doesn't mention that the iMessage blue also fails the same WCAG test. I just ran it myself.

As shown in the image, the blue at least passes the test for "large text"

Your hex value was sampled from a screenshot taken in dark mode, and actual color values are slightly different between dark and light mode.

This is not true. I just sampled green bubbles from both dark mode and light mode iOS and macOS and got the same hex of 34c759.

Ah you’re right. I stand corrected.

A comparison between blue and green bubbles on your phone would be more relevant. Color space handling makes direct comparisons between screen grabs tricky.

The author used the screen grabs from different places too. On iPhone you can't have the blue and green bubbles side by side

A reasonable start would be screen grabs of both blue and green bubbles, grabbed from the same phone in the same way. (And vertical placement; see the other comment.)

Here are the results for your image. Contrast still fails on WCAG guidelines.

https://ibb.co/sKfrZ16