This has nothing to do with NetzDG. If he would have spewed something of that caliber openly on the street he would've had to expect the same thing (depending on where in Germany of course).
That there is no "free speech" in Germany in respect to hatespeech has been the case pre-internet too. I'm not a big fan of NetzDG, but I also have to say that I expected much worse censorship-wise when it passed and I haven't heard of gross misapplications of it so far. If anything Facebook and Twitter show that you can still post a lot of hatespeech despite its existence.
You can do many things: You can pass those laws, put people in jail, make up the term "hate speech" and condemn everyone who does that. But you can not say that we have internet (or any other) freedom in Germany. There is some nice english proverb about a cake and eating it too
You can try to argue that certain things aren't "hate speech" but I don't understand how you can claim it to be a made up term. Hate is a real thing and if you channel that into certain language you get hate speech, plain and simple.
Germany has an interesting history with regards to what various constituents view as protected speech. As someone who hasn't lived in Germany I freely admit that I have a limited view of such things, but as the other poster mentioned these issues precede the internet.
hate itself is real - a word that has a negative connotation, but was never illegal in itself. You could always hate a person or a football club. That word was taken, rebranded to include among other things everything critical of government and made illegal. That's why hate speech is made up. What is called hate speech today was called a rant, "hot take", an insult or whatever just a couple of years ago. Today we literally have a law against "hate crime" - another doubleplusgood word. These things are not real, they're tools to oppress a critical population. Also note that even true things fall under those "crimes". It doesn't matter if what you say is true as long as it's "insulting" to someone.
That there is no "free speech" in Germany in respect to hatespeech has been the case pre-internet too. I'm not a big fan of NetzDG, but I also have to say that I expected much worse censorship-wise when it passed and I haven't heard of gross misapplications of it so far. If anything Facebook and Twitter show that you can still post a lot of hatespeech despite its existence.