You've got what there, 10^16? That is certainly a very big number. But then, the article is claiming that the chance of becoming complex is a very small number. Is it less than 10^-16? (Is it even knowable? At a minimum, the author thinks he can say something about it.) You'd be surprised how fast these numbers get small if you need to brute force yourself away from a local maximum and over a valley.
I don't care how big your bignum is compared to everyday experience. Bignum * Smallnum does not automatically equal certainty, impossibility, or feasibility. It means do the math.
All of them are eating. Some of them are mutating.
Let them do this for a few billions of years and what seems to be a very unlikely event suddenly becomes almost certain to occur. Complex life FTW!