I think it's a bit unfair they call it just "paint" when it was merely cornstarch that would wash off by itself.
There's a huge difference in the degree of vandalism if it's something that wash off by itself.
It's possible. And I think it's likely. That the activists wanted this exact news cycle, where they falsely report that there is damage, gaining widespread coverage, and drawing attention their way, only for people to later learn that it was temporary and grow to respect the act.
Possibly. I'd imagine the vast majority of people don't see the followup that there wasn't damage, here, or the Mona Lisa, or the other events. The goal was outrage coverage for sure, and without causing damage so anyone who actually cares is fine with it. The media will just call it paint, and now that the potential for damage is clear they'll stop talking about it.
Media uses language like this on purpose, most of their copy comes from single-sources and everyone on every news station is repeating the same rhetoric. They did this with the soup/painting incident as well, making it seem like the protestors ruined priceless artifacts instead of spilling harmless food products on a sheet of plexiglass.