Is this calculation of mining probability using the Bernoulli trial formula accurate?
The formula is a reasonable approximation.  It looks to me like your calculation is right, and the blog author has made an error.

There is a minor inaccuracy in that the number of blocks per month is not fixed at 6*24*30, but is subject to random variation.  So a slightly improved solution is to work out the average number of terahashes needed for one block (h = 11000000 * 600, assuming that the network hash rate is stable and the block difficulty has adjusted accordingly).  Then your probability of winning a block on each of your hashes is q1 = 1 / h, and you will perform M = 12.5 * 60 * 60 * 24 * 30 hashes in one month.  If you treat the number of blocks you win as a Poisson distribution, the probability of winning one block in a month is given by λ * exp(-λ) where λ = M*q1.  This yields the slightly larger number 0.005273.