Do bugs in Houston tend to come inside in October? If so, the ad may just have been targeted at location + time of year. (I'm just tossing out a hypothesis; I have no opinion either way as to whether Facebook was listening.)
All you need is some more or less benign targeted advertising by local exterminators (for example, "age 22+", "females and married couples", "single-family dwelling", and a zip code the exterminator knows have had lots of bug complaints) and somebody happening to glance at their phone after being spooked by bugs.
(You may be creeped out by Facebook knowing what type of dwelling you live in, but that's a separate issue.)