Not to mention him saying no one writes java anymore when it literally powers world's most popular OS (android) and double digit percentage of internet backends
core (as in kernel) is running linux kernel which is C, yes.
But java is not 'just UI' - majority of user space apps run java (or jvm, to be precise), as well as tons of system services, to the point where you can't actually do a lot of android API calls from native code, because a lot of logic is written in java(or kotlin) code, and not just java being wrapper around native code.