The build-X-in-low-Y-minutes trope implies that something is trivial to implement (usually by importing middleware that does the heavy lifting). A 30 line class is not trivial.
> The build-X-in-low-Y-minutes trope implies that something is trivial to implement
I think it just implies that the reader can do it without prior knowledge, and that Y minutes is surprisingly small.
You wouldn't write "build a blog in 80,000 minutes" even if it could be done with one line of code. And you wouldn't write "build [complicated thing] 3 minutes" and then show an expert rapidly typing a pre-determined program into an editor.
If a newbie can do it in Y minutes following the tutorial, it seems valid to me.
EDIT: This comment was not appropriate, I apologize.