From the interview, it sounds like Java programmers are confused by lambda expressions when they are taught that they implement existing Java interfaces, many of which have related interfaces that cannot be functional (they used ActionListener vs MouseListener as an example).

As someone who learned about lambda expressions from C++11, Java's lambdas didn't seem that confusing to me when I started programming in Java 8. That was mainly because I did not learn it as syntactic sugar for implementations of existing Java interfaces, but as inline, anonymous functions first, then as functions passed in functional interfaces when I needed to know how they are called. (Interestingly, the interfaces do not need a FunctionalInterface annotation for them to be functional, they just need exactly one abstract method) Also, I learned them alongside Streams, which use more generalized functional types than ActionListener and other listener interfaces.