ZD – If someone came late to their chavrusa because there were pedestrians crossing on a crosswalk and they had to wait for them, you wouldn’t blame the pedestrians. If they were held up because there was a lot of unexpected traffic because of a Simcha, you wouldn’t blame the baalei hasimcha or the people attending the Simcha.
If you were late to a chavrusa because the streets were closed off because the President of the US was visiting, you wouldn’t blame the President. If the streets were closed off or blocked because of a Yom HaAtzmaut parade, you wouldn’t blame the people having the parade.
In Israel, protests/demonstrations are a normal, common, accepted practice, and they are held for all sorts of reasons by all types of people – left wing, right wing, secular, religious-zionists, and Chareidim.
This being the case, I am not sure that they are any different than any of the above examples. Of course, one must ask a sheilah since, as you correctly point out, there may be several halachic issues involved. But it is very possible and even likely that there are Gedolim/Rabbanim who allow and encourage demonstrations in certain cases. Therefore, there is no reason to assume that these boys did not ask a sheilah, and in fact, it may be assur to assume that they didn’t.