Actually he discusses his reason, right there in the post. Spotify used a lot of his bandwidth with no way to throttle (as others on this thread have discussed), in a way that he didn't feel was disclosed up-front.
It's great that you love Spotify and get value from it, but don't jump on this board calling someone a liar and questioning their integrity because they don't get the same value from it.
But, to the point, he never said how much traffic he was seeing, so in his case /any/ traffic could be deemed "a lot". All services these days use your network connection to some extent, but I'm finding it hard to believe that it actually may end up congesting your networking connection, without seeing some serious proof.
I can to some extent see his point where this should've been clear from the start of, that Spotify will make use of your upstream network connection. Hopefully Spotify will make changes so that at least the US-market get notified that they might end up paying their service provider a premium, just for using Spotify.