Without seeing screen-shot cant tell you 100% - but I think this one sounds like smart play rather than rule breaking. I will explain.
In temperate (I am guessing this is) the game mechanics to grow a city as fast as is possible is to have FIVE stations (or bus stops, airports whatever) in a city taking stuff regularly
see:
wiki.openttd.org/Towns#Town_Growth
There is nothing wrong with having 5 stops to grow a town as long as you are not blocking off a town to other players, or breaking other rules.
PS we have lowered city growth so this wont work as well at it used to