I can't speak to this specific teacher, but as an art school grad I can say there is a really sad strain among teachers to denigrate anything a) pleasingly figurative, and b) commercially successful. Thomas Kincaid is painted with the same brush, his landscapes are conventionally pretty, if a little kitschy, and wildly lucrative.

A surprising number of fine arts professors in modern art schools couldn't draw a convincing likeness if they tried and fewer make a healthy living so there is a tendency to snipe at those more successful.

"Art School Confidential" is a great movie if you want a picture of what it's like at art schools today.