Look at Newton's Early life (0) and we can see that he did not 'make a bet' with his life. Though he managed to get into Cambridge on a scholarship (an element of luck), he was considered 'undistinguished as a Cambridge student.' His 3 really big accomplishments (optics, gravitation, calculus) were generated when he was on break for 2 years from Cambridge due to plague. The question we then must ask is: what would he have done otherwise? It's a 'bet' if there is an element of risk, though it seems this discussion is more about what different English speakers use the word 'bet' to mean. What were the downsides to just poking about with math and lenses in your 'free' hours? Maybe he missed out on some farming/church duties or he traded this time to do Optics instead of gossiping. I don't know. What did young mid-17th century celibate Englishmen do in those days while hiding from the black death? Tennis? Point is, he wasn't really risking anything but a little bit of time spent in the mid 1600's English countryside that he had to spend out there anyways. A 'real bet' would have been staying at Cambridge despite the plague to work on Optics with the professors, as the risk there was quite clearly your life.

(0) https://en.wikipedia.org/wiki/Early_life_of_Isaac_Newton