I had read it before, and I skimmed it again just now. I think this is just Feser redefining cause so that its meaning is so broad as to have practically no content, and to make the claim that everything must have a cause trivially correct. The cause for the decay of the atom is now whatever made the atom, or inherent in the atom’s existence or nature.

This does nothing to change my description of the decay event as being an uncaused event, for more interesting notions of “cause”. And I believe that it does throw a wrench into the argument for the necessity of a first cause. In short, what Feser lacks in brevity he fails to make up for in persuasiveness.