Pure coincidence. Had there been a way for the cats to get out by themselves, they would have bolted and the people would have died.
Oh really?
http://www.animalsentience.com/news/2003-10-16.htm
Cat saves lamb from drowning
A lamb who escaped from his pasture in England was saved from drowning in a swimming pool by an alert cat.
Puss Puss, a black and white cat, discovered the lamb's predicament and frantically meowed, running back and forth between the pool and the garden where her owners were working, to alert them to his plight.
Puss Puss's owners, gardeners Adrian Bunton and Karen Lewis, had taken her along with them to work at the garden of Cotswold District Council chairman Tim Royle in Cheltenham , UK . Jill Royle said, "She was in a Cat saves lamb from drowning very, very agitated state, meowing and calling and crying and being an utter pest and dashing back and forward between them and the pool."
When Bunton and Lewis found the lamb he was under the swimming pool cover and his head was entangled in the pool cover straps, which actually were keeping him from drowning. Bunton jumped into the pool to rescue the lamb while Lewis went to get help.
Puss Puss is "a real little superstar," said Lewis. The actions of the quick-thinking feline are all the more remarkable because she is disabled. "As a kitten she had an accident and had to have her tail amputated, " Lewis explained. "She hasn't grown properly, has arthritis and can't curl up, jump or climb like other normal cats."