In 2017 Bryan Cantrill gave a wonderful talk titled "Platform as a Reflection of Values: Joyent, Node.js and Beyond" https://vimeo.com/230142234 In it, he talks about how even though they liked JS as a technology, they came to realize that the values of the JS/Node.js community differed from their values at Joyent.
In the talk (at around 19:30), he identifies that in 2014 Joyent's core values wrt node.js were "debuggability", "robustness", and "stability"; while the core values of the broader node.js community were "approachability", "expressiveness", and "velocity". And there's nothing wrong with either of those sets values, but they're not the same!
With that lens, I'd characterize the parent comment as contrasting the PostgreSQL team's core value of "robustness" with the Javascript crowd's core value of "velocity". That's a distinction in values, not in technology.
It's not entirely about persistence... it's about the ease and reliability of the persistence.
The people behind javascript provided the object notation technology that has been absorbed by Postgres. It is not only being used to exchange data (as a standard text field would be used), but can be used to QUERY data. The database is aware not only of the JSON text string representation, but of the object itself.
Wait until this guy learns what the JS in "json" column types means, and how the largest webcrap sites rely on them for persistence.