To be precise, he thinks they're anti-authoritarian, for which "terrorist" is the long-established authoritarian code word.
I had to look this up, the word doesn't have a very long history claims this bit https://www.merriam-webster.com/wordplay/history-of-the-word... . The first authoritarian regime that might come to mind to most after the French Revolution, the Nazis, didn't use this word commonly for their opposition, either, AFAIK.
?? you think no government between the French Revolution government and the Nazis could qualify as "authoritarian"?
[0] https://www.hstoday.us/featured/how-autocrats-exploit-the-de...