It suggested an 11% reduction, which is in the ball park of other research.
The scientific consensus comes from other studies, to which this adds.
This particular study showed a trend, that was in the direction of the other research (the other research suggests that masks are effective).
They need to do a larger study using similar methodology to get the statistical significance.
It's quite common in scientific studies to have a smaller piece of work show a trend and then a larger piece of work follows it up.
Since the decision to use masks in school was not made on the basis of this data, but on the other previous scientific consensus, the basis for that is unchanged.