DESCARTES AND RUSSELL
I think you are quite right to be puzzled. I believe that, when Russell wrote the above (he changed his mind on all sorts of topics, so one has to deal with-- as it were-- more than one Russell), he rejected a philosophy of substances and, instead, proposed that the concept of an event is more accurate. So, in another essay or book, Russell charged that Descartes' inference "I think, therefore I am" begs the question. It assumes the very thing it sets out to argue for. Russell thought that Descartes should rather lay claim to this thesis: "There is thinking." Such an event does not (according to Russell) commit us to positing a substance, the thinker, just as the statement "It is raining" does not commit one to holding that there is a thing that is raining. His absolutely mind-blowingly bizarre comments on cannibalism to one side (what evidence could Russell possibly be relying upon), Russell is claiming that our "common sense" inclination to think in terms of substances is owing to our use of language with subjects and predicates. Is Russell's position plausible?
I think his position is quite suspect. Recall that Descartes set out to doubt all that he could. He imagined an all powerful deceiver who might deceive Descartes into merely thinking he exists. He finally came to the point where he found his own being unmistakable, for he concluded that he could not doubt he existed unless he exists. Indeed, I suggest that our awareness of ourselves as thinking, acting, feeling, etc beings over time is self-evident. Contra Hume, I suggest that every time you feel pain or see red, you aware of yourself (as an individual subject) feeling pain and you are aware of yourself seeing red. Back to Russell: I do not think we can make sense of there being a state of affairs of 'there is thinking' without there being a thinker. This is not a reflection of a merely contingent characteristic of language. It makes no sense for the event "running the New York marathon" to take place, without there being runners. Yes, we have the words "running" and "runner" but to suppose you could have running without runners is a logical or conceptual point. It also seems misleading to think the event "It is raining" is utterly void of individuals or substances --be they clouds or water droplets or H20.
There is not a huge consensus on the nature of events today, but a common one is that an event consists of an individual or individuals and at least one property such as "People thinking." Some philosophers think an event also needs to add a time. And I must note that while my own judgment is quite solidly Cartesian contra Russell, there are a range of thinkers who have sought to dispense with individuals and put in their place processes or fields or (as Russell does) events. Nelson Goodman once (I believe) observed that, in his view, the White Cliffs of Dover, is an extremely long event.