I interpreted the Whitehead quote to mean that you should seek the simplest explanation that explains whatever it is you are trying to explain. This is consistent with Occam's Razor. I assumed that "distrust it" meant subject the explanation to additional tests to confirm or falsify the explanation. So, I didn't see this quote as contradicting William of Occam; instead it built on Occam's Razor to describe the essence of the scientific method.

This interpretation is supported if you look at the context of the quote:

The aim of science is to seek the simplest explanations of complex facts. We are apt to fall into the error of thinking that the facts are simple because simplicity is the goal of our quest. The guiding motto in the life of every natural philosopher should be, "Seek simplicity and distrust it."