Hello,
Thank you for both of your comments.
First I should apologise for some of the figures in the article are not clear enough. I should find time to change them.
Second, as for your question. Take the following convention: When you are at a state, you only look ahead, to what might come from future states.
The value of a state is defined ONLY by what future values/rewards it might receive.
Regarding S2, as I said the figure is confusing, what does actually do, is zooming into S2, such that you are at S1 and you hit the blue you arrive at S2 with 50 points, and if you hit the black you arrive at S2 with 10 points. Again I agree it is confusing and should be changed.
S2 is a terminal state.

Hope it is clearer now.