I believe in this case he might be confusing
pbinom indeed gives same result over any number of replications.
pbinom(., n, p) calculates the CDF of
Bin(n, p) distribution, whereas
rbinom(., n, p) generates (pseudo) random observations from the same distribution. So, to get reproducible results,
set.seed can be used. But as CDF uniquely characterizes a distribution, so
pbinom will always return the same result.