Ethan is being disingenuous here. CPS did not get called because his son had diarrhoea, they got called because he said his son had caught giardia from his dog, having previously established he lets his dogs shit in the house. Now he didn't specifically say "he's been diagnosed with giardia", but he talked at length about how the dog had diarrhoea as a result of giardia and they'd only just started treating it, that his son is crawling and puts things in his mouth, that "now Sonny has giardia", and then talking at length about how stinky and messy his son and wife's diarrhoea is (because Ethan is disgusting).
While he is now saying that his son does not have giardia and his house is super clean actually, that clarification only came after the CPS call. He very much is at fault as to why CPS got called.