What you are blocking with that filter is everyone that visits from sitepoint.com; i.e. the guys at sitepoint.com, probably.
To exclude all visitors that came from sitepoint.com as a referrer, see https://support.google.com/analytics/answer/1034842?hl=en
Also, beware that filters don't work retro-actively, they only work on future data.
So it's always a good idea to create several profiles for a property and have at least one profile without any filters whatsoever so you always have access to raw data from the past.