Spartan,
Quoting the rules, and enforcing the rules are two different things. You are correct that one finger can control the ball, but if the ball is still moving/rolling/oscillating in any way, it is not under control. A keeper has to have the ball in "control". This can be considered two hand control, hand to body control, hand to ground control, or even hand to post control. Those are your options. If the ball was rolling, or the keeper had it with one hand, and tried to pull it into their body, by moving it, a referee could consider that not in control by the way that the keeper decided to move the ball. This is one of those rules that is "in the opinion of the referee". So it is determinate on the referee that you have, and their intrepretation of "control". What fun, what fun....