High levels of wear metals with normal purity classes?

How can there be high levels of wear metals with normal purity classes?

For years we have been using your analyses to monitor the hydraulic fluids in our excavators. Poor oil purity, contamination or excessive water content have been found repeatedly. However, we recently received a laboratory report from you which shows high wear values but completely normal purity classes, to our considerable surprise. Shouldn't the purity of the fluid be significantly worse with a relatively large increase in wear metal?

 

Source:

OELCHECKER Spring 2013, page 8