I don't understand this sentiment. I understand Kotlin has more features than Java, and of course it's tough to call the advanced things from Java. At least so I would think.
No he was not right. You can write two-way interop and it is not hard. I have actually written a library which does it. He did not say that "the two-way interop is not seamless". He said that you "can't write two way interop code" which is not true.
So basically, he was right, and you weren't. There is no seamless 2-way interop, yes?