Without looking more at the variants themselves and just going by the numbers in the post, it’s entirely plausible. It’s not likely, but plausible.
Mainly because we are talking rare events. If the level of success is 33/3.5 (9.42), we’d expect that 4 (or less) silent variants would happen with a probability of ~ 0.042 (Poisson X <= 4). So, a bit more than a 4% chance. But with millions of people infected, this ratio of S/NS variations would still happen at a pretty high absolute number.
Anytime you look at numbers like these, remember with a big denominator, even rare events are expected to happen.
