Having made a starter, you most likely have very active yeast and you don't have much headspace in the carboy so the extra activity causes more foam. That foam has to go somewhere, the only outlet is the neck of the carboy.
It looks like you controlling the temp with a water bath and ice (in some form) which will help slowdown, but not stop, the blow off.
The picture makes me think you are doing fine. The activity will slow down in a day (or two).