Ooh, this should help: I just found the formula they use to calculate activity points. You can use this in the meantime, until you get a slider:
Activity points for light intensity = [your weight] x [minutes] x 0.00023
Activity points for moderate intensity = [your weight] x [minutes] x 0.00033
Activity points for high intensity = [your weight] x [minutes] x 0.00081
You could stick those in an Excel spreadsheet if you're handy with that sort of thing, make your own little calculator.
As for your walk, it should net you 2 points.
(EDIT: That's according to my slider, you are firmly in the 2 range. Using the formula, you end up with 1.7. I guess the slider rounds up?)