How did they target the group though, did they just scan the internet traffic and said, oh wow there is a group of people who only talk through Signal, or were there another precedence?
[1] https://fr.wikipedia.org/wiki/Affaire_du_8_d%C3%A9cembre_202...
They were then arrested preemptively (after the surveillance was retroactively authorized by a judge!) and one member was held in solitary for 16 months. Despite all that, the prosecutors apparently couldn't find an actual plot to accuse them of planning, so they're pointing at their use of Tor and Signal instead. It's pathetic.
them fighting alongside YPG has nothing to do with why they were arrested, it's just backstory.
That's not correct. One person fought against Daech in Syria, then a few years later a dozen persons get arrested ; most of them don't know one another. You can't really talk about a "group" and certainly can't say they took arms when only one of them did (and for an arguably very good cause which was approved by the State on paper).
I agree with you the video title is misleading, though.