Earlier quoted context omitted.
If I was from the police I'd probably want to block the chance to coordinate such attacks, not only do an investigation to track certain individuals. What would be the point to spend many resources to put a guy or a few of them in jail when they can be easily replaced.
Of course it depends how many people are involved in such things, and whether the app specifically is allowing them to coordinate these attacks. Most of the commentary so far has been about demonstrations, sometimes turning into violent riots. Purposely sabotaging/obstructing a piece of critical infrastructure is something rather different, although whether it could be defined as "terrorism" is somewhat ambiguous.
I won't define it as terrorism, but if you are in the Police and you really have no other legal tool, what do you do? If the boundary is fuzzy enough, they're gonna push for it.
In the end they'll probably have a hard time proving that to a judge, but as a temporary measure they probably think it's useful.