Its genetic. If you breed one like that it can show up in pups later. But look it up it is for sure genetic. Clifford's mom smiled and would bite !! Ha ha. Had a old strain of rat terriers years back that a bunch of them smiled.
I say it darn sure is....
I got a red bitch pup here, whose momma "smiles" for certain folks when she's happy to see them....and sure enough...my lil pup smiles at me even harder than her momma does, lol. Far as I know, she's the only one in her litter though that does it.