I read it and there's no way I would ever clean it with soapy water. That is absurd. I do make sure the filter is dry (almost) prior to installation. After all, what is happening to the air that passes through? It immediately gets mixed with gas, then goes into the cylinder.
BTW, the manual also says that the flock filter is for use in dry dusty conditions. I never cut in those conditions but after more than a few carb clean-outs where I found sawdust chunks, it's the best filter to keep crud out of the carb. I still find some, but much less. Personally, I think the air filter design of Stihl is not nearly as good as it should be. There should be zero wood particles getting through.
