Caution! If you compare across languages like that, not all virtual calls are implemented equally.
A C++ virtual call is just a load from a fixed offset in the vtbl followed by an indirect call. This is fairly cheap, on modern CPUs pretty much the same as a non-virtual non-inlined call.
A Java/C# interface call involves a lot more stuff, because there's no single fixed vtbl offset that's valid for all classes implementing the interface.
Yes, it is true that there is difference. I'm not sure about JVM implementation details but the reason the comment says "virtual and interface" calls is to outline it. Virtual calls in .NET are sufficiently close[0] to virtual calls in C++. Interface calls, however, are coded differently[1].
Also you are correct - virtual calls are not terribly expensive, but they encroach on ever limited* CPU resources like indirect jump and load predictors and, as noted in parent comments, block inlining, which is highly undesirable.
* through great effort of our industry to take back whatever performance wins each generation brings with even more abstractions that fail to improve our productivity
