Most houses with crawl spaces have entry points to get in for maintenance of stuff like plumbing and HVAC. And vents for allowing air circulation. As houses get old, these are often compromised and critters are attracted to the warmth in winter.
Most common design of houses in the SF-SJ Bay Area of CA. Snakes are generally not an issue in that part of CA. But skunks and raccoons are, and if a female skunk gets under a house during the January-February time frame of their mating season, the resulting smell is brutal. This is particularly true if the skunk manages to find a weakness in the HVAC duct-work and crawls inside for warmth while the heater is running.
The house in the article must be an old design in TX, or at least in that part of the state. In and around Austin, seems nearly all of the houses built in recent years are on pretty thick slabs.