So? It's still vandalism. Just because OP got to it before a Wikipedia mod did doesn't mean it's okay. Also, OP has no clue how popular any one article is nor who is looking at it. If someone saw the vandalism between the time the article was first changed and the time of the class that makes Wikipedia, an almost entirely volunteer led project that many of those volunteers are very proud of, look bad.

I'm sure no Wikipedia editors would care if someone created a new account and did that demo on that new account's user page. Especially if that person was upfront about it on the page. But doing it on a public Wikipedia article is a dick move to people who volunteer their time to keep Wikipedia clean.