Are “function types” more or less “functional interfaces”?

Hi! I’ve been reading about function types in Kotlin and I came across this article that says:

Function type is just a syntactic sugar for an interface, but the interface cannot be used explicitly. Nevertheless we can use function types like interfaces, what includes using them as type arguments or implementing them

Here

And I do really see it, but because this is the first time I’ve come across someone claiming that function types are syntax sugar for functional interfaces, I’d like to see what other Kotlin developers think of such statement.