Ah yes, we'll save the planet by writing web services in Rust, which serve inefficient, bloated webapps to billions people, with browsers constantly spinning the CPU near thermal shutdown...
If you want to save energy, write small software. Small, local, self-contained software. Not everything has to be a webapp. In fact, most things shouldn't.
I think they were just pointing out that software architecture will usually make a much bigger impact on efficiency and energy usage than language choice
A bloated app is wasteful no matter what language its in
For most use cases JS is still more performant than WASM unless you're doing a lot of very heavy number crunching which the vast majority of WebApps aren't.
If you want to save energy, write small software. Small, local, self-contained software. Not everything has to be a webapp. In fact, most things shouldn't.