I did as you suggested.
The article states that he has been writing anti Islam rants for several years.
We know he didn’t learn this recently.
A good bet as to where he learned this is from the Koran itself.
Here are a few passages. There are many more.
2:191-“Kill them (unbelievers) wherever you find them. Drive them out of the places from which they drove you, for persecution is worse than slaughter…. Such is the reward of those who reject faith.”
2:193-“Fight against them (unbelievers) until there is no dissension, and the religion is for Allah.”
Fight until no other religion exists but Islam.
3:151-“We will throw terror into the hearts of those who disbelieve.