I also noticed this in IntelliJ when I went to copy some Java into a Scala project. As I began converting the Java code to Scala after the copy I was extremely confused when I found that the pasted code was already converted for me.
That being said, it doesn't work very well in many circumstances. I'm not sure if they're using Scalagen under the hood or their own home-baked stuff. It's impressive as-is, regardless of the issues.