It's not that they're failing to wash their hands 10% of the time, it's that they're not washing their hands properly 10% of the time. We don't know if the incompleteness is significant or insignificant.
However, I would consider bad hand washing almost as neglegient. It's really not rocket science
Blaming healthcare providers for not washing their hands is like blaming John Q Public for the housing crisis. The reality is much, much more complicated, and solutions to the problem are equally so. Healthcare is an incredibly complicated ecosystem, and even things are simple as hand washing are affected by dozens of factors, many of which are non-obvious at first. Root cause analysis and a judicious application of process change can help greatly, but the reality is that even simple things such as this do not change overnight in healthcare. It's harder than you think.