Could say that bad things happen in any number and it would be correct since there is no time period associated with it other than "real soon".
It would maybe mean something if the saying was "bad things always happen to fat people" or "bad things always happen within a 4 hour span of each other on Thursdays".
Otherwise it is just another case of the human mind being designed to notice patterns as a survival mechanism left over from when we needed it and it is easily confused by today's excess of information thrown at it.