If they are doing Kotlin/Spring, they are using Java no matter what.
It is like using Web and avoiding JavaScript, or UNIX and avoiding C/C++.
Sure it is possible to pretend it isn't there, until one needs to do serious stuff that requires understanding the platform and its ecosystem.
By the way, once upon a time Spring was also all hot on Groovy, then it was Scala, now it is Kotlin.
There is a certain irony complaining about Java programming language features and them going into Go, the epitome of programming language design.