Trunk-based development, as I've seen it explained in the past, isn't what that site describes. The way I understood it is, no branches at all, everything committed straight to trunk, and extensive use of feature flags to keep incomplete features hidden.

Short-lived branches like that site's describing just sounds like a team that's adopted git pretty well, but not formalized usage into gitflow or similar...

It’s trunk driven because there aren’t some long lived branches like ‘dev’ and ‘staging’ or ‘release-xx’

Feature flags can be used to gate features until they are ready, but all code is committed to trunk and is deployed to prod mostly continuously.

What’s the benefit of having release branches without commits if you can just use tags? I guess the difference is mostly cosmetic?

It's optional, I guess because so many companies or teams would immediately discard TBD if this wasn't addressed.