Key words here are "over the study duration" and "over the time period of the study". The study started in late July, so it's been about 4 months. The data that they examine probably lags a bit too and in the intervening period, cases have gone up significantly.

Over the course of a longer period of time and with cases on the rise as they are now, I'd expect the risk reduction to be much higher.

Edit: Also, these numbers are somewhat skewed by the fact that not all 40k people got the vaccine/placebo at once, but over a period of time.