What likely happened: Developer needs an official MBTA map. They do an image search. That map is one of the first five results. They take it from there and use it. Seems like getting " fucking furious " is a bit overkill.
I wouldn't be surprised if N.D.'s official policies are much stricter, and would normally call for any art to be freely-available/purchased/redrawn/etc, but in this case the artist found a map, had a tight deadline, and thought to himself "oh, all these maps look the same, who's gonna notice"...
[The answer obviously is: "Transit map nerds are gonna notice, that's who...especially the one who drew the map..." :]
I've read the Transit Maps blog for ages, and it's a great blog; over the top or not, the reaction's kinda in character... oO;