Overall calories matter as a piece in the puzzle, and if he said that or even said they are the foundation, he would be right. he didn't. He said only thing that matters is net calorie intake.
You said 'most important'. Congrats! You aren't building strawmen.
And that is KNOWN to not be the case. There are many other elements at play. You as a fitness professional would know this. The type of workout, the type and timing of cardio (if any), the macronutrient ratios inline with your goals. As I said, if the only thing you care about is 'not being a fatass' and the number on the scale is end-all-be-all, calories are probably fine. Though, if you want some size, or definition, or abs, or performance, or any number of other things, calories don't tell the whole story.