It's subtle misinformation that's designed to change how people unconsciously perceive PWAs. When people bring up PWAs, they commonly refer to a particular set of APIs which has a tendency of mainly being a Google-driven effort. GP is muddying the waters by instead framing it as the HTML spec itself and implying it's official.
If this isn't a clear case of gaslighting, I don't know what is.
I'd argue this is a lie and not an example of gaslighting.
A lie is simply stating something that is not true. In this case, stating that HTML5 is synonymous to PWAs.
Gaslighting is an attempt to undermine an individual's (or perhaps even a group's) certainty that they are able to perceive reality correctly. It's essentially an effort to make someone question their own sanity. Lying is a tool that may be used as part of this effort, but it is not the only method of gaslighting.
It's also possible to lie without gaslighting. Speaking mis-truths may happen accidentally. But trying to cause someone to believe something that isn't true, isn't necessarily or inherently an attack on their trust in their own ability to perceive the world.
In this case, I can't see any indication that the goal is to cause anyone to feel insane.
If this isn't a clear case of gaslighting, I don't know what is.