That more or less what I said, it is not incompatible as you can use the Java stream API if you target Java 8. But yes, it is a pain when you see you have to use the Java Stream API instead of the kotlin Stream API.
Not incompatible but an issue. And they seem to have resolved it. Look at last comment. What you are quoting is from December 14th, before even the initial 1.0 release of kotlin.
Like I said, Kotlin is chasing after a moving target. The issues might be kinda-solvable (even if it requires significantly diverging from Java's APIs), but things inevitably get messier both for the language internals and for users.
Not incompatible but an issue. And they seem to have resolved it. Look at last comment. What you are quoting is from December 14th, before even the initial 1.0 release of kotlin.