Not a math fag, but I think there's a problem with this approach. I remember something about the odds of rolling doubles with dice. If you are asking what are the odds of rolling two ones, 1 in 36, then this math works, but if you are asking for the chance of rolling any double with a six sided die, then it does not work. The odds of the first die rolling a number is always 1, so the odds of a double are just the chance of the second die matching the first which is a one in 6 chance, not a one in 36.
I'm pretty sure that the same logic applies to the chance of a Q post matching a Potus tweet.
With 4642 Potus tweets we'd need to calculate the probability that ANY 18 of the 2969 Q posts would hit at the same time.