My Meiwa are not really juicy either. The "Hardy Citrus for the Southeast " book by Tom McClendon says about Meiwa, "with a tender peel and very little juice." We eat Meiwa for the sweetness of the peel. I think of them as citrus gum balls. The only weird thing I find about eating the kumquat is chewing up the seeds, otherwise I find the Meiwa quite enjoyable. Maybe your fruit got some frost damage that caused the pulp inside to shrivel. I noticed one of my grapefruit had dry shriveled pulp that was dry after freeze damage.
Well I could tolerate little juice, but no juice at all and dry pulp make it an unpleasant experience very dry in the mouth.
Even an apple it's not a fruit that you would think of juice when eating it, but if it was completely dry it would ruin the flavor.
Had the same idea about frost, but seemed strange since it was from a nursery specialized in citrus.
Maybe since it is hardy it was kept outdoor to save space for other plants, who knows.