That sentence is wrong to imply that there is anything special about data versus method attributes with respect to overriding -- or that attributes are special when it comes to names in a single namespace. What I think the paragraph should say, if not just deleted, is something like.

"Instance attributes hide class attributes. Instance data names are often intended to override class data names. But instance data names masking methods names is likely a mistake. This can be avoided by using verbs for method names and nouns for data names."