Greenfoot IS real programming. Greenfoot was made to make it easier to start programming. The only difference is that Greenfoot makes it so that you can focus on your code by providing a way for most things to "work" easier. Then, when you want to move on to more complex coding, just import another API into your project (adds more possible codes, etc). Really you're free to do almost anything Java can do within Greenfoot, though by the time Greenfoot is limiting you, you will be more than ready to code Java on your own.

The language you're using in Greenfoot is plain old Java - you can use any Java libraries you like, code just as you would in real world Java - the conventions are the same, the syntax is the same, the language is the same. In short, pretty much all the concepts you learn in Greenfoot can be applied to "real world" situations, Java or not - and if you develop using Java (which is a highly used language in the real world, Google uses it extensively for instance) they'll translate directly. Greenfoot does make things easy from a graphical perspective and there are of course additional concepts that you will learn if you migrate outside of Greenfoot. But yes, Greenfoot is definitely real programming and it will definitely give you good programming practice!