I'm reading in it that experienced developers (be it overall or in a specific codebase) "know" all the ins and outs, types, conventions etc, whereas less experienced people cannot yet know all of that; being able to lean on good types and / or other types of automated checks helps them make more confident changes.
Less experienced devs iterate on something until it looks like it works, not realizing the footguns they may have embedded. Static typing removes some footguns and provides documentation for the next unfortunate soul to look at this code.
