It's going to wash off next time it rains, so I think it's a cute way to "inaugurate" the new bike lane. If it were permanent I think I'd feel differently about it (not that I have any strong feelings since I don't live there) since it does look cluttered and unprofessional (but I suspect that was part of the point).

It's not vandalism if you have permission (the article is unclear on that point). I'd say this particular instance, even if it wasn't sanctioned, would be on shaky footing for any legal vandalism proceedings: there's no malicious intent, it washes off with water (so if someone's really unhappy, take a hose to it and it's clean in what, 30min? Bet the people that did it in the first place would wash it off if it was an issue), and I doubt it could be argued that it caused significant damage to the property (there's a dollar amount that you have to reach before it's vandalism).

IMO public art is art that's in public view. Typically with the connotation that it's sanctioned and wanted (that doesn't mean it's good, or that everyone is happy it's there, etc. I walk through parks all the time with metal "art" (done by artists) that I wouldn't mind in front of some modern building, but I just can't bring myself to like in the middle of nature, but that's my problem.). Graffiti can be public art (it's not always scrawled on back alley walls without permission) or it can be vandalism.

I'd call this Graffiti that is much more towards the public art side. I just can't imagine someone that's not already angry and unhappy with life being horribly upset by purple dinosaurs and "thank you" messages that will be gone shortly anyway.