The theory has not been tested on domestic cats yet, but research on western scrub jays in 2012 showed that seeing a dead member of their species led them to produce alarm calls and behave in ways that were similar to when they would avoid a predator.
Additionally, a study on bumblebees in 2006 found that they were less likely to visit flowers that contained the body or scent of a freshly killed bee, a strategy that helps decrease their chances of being attacked.
This suggests that cats may be acting on a survival instinct. Some of the owners who participated in the study noticed that their cats went into hiding or sought higher vantage points after a fellow pet died, which could support this idea.
The study was published in the journal Applied Animal Behavior Science.