https://www.latimes.com/health/la-xpm-2011-may-16-la-he-fitness-muscle-myth-20110516-story.html

Seems like its a “technically true” but in practice irrelevant because muscle and fat only make up a tiny percent of total energy usage (because things like the brain, heart and liver are so energy intensive):

For fun, let’s run the numbers in even more detail, adding the role played by body fat. Bouchard sent me a follow-up email explaining that — based on the biochemical and metabolic literature — a pound of muscle burns six calories a day at rest and a pound of fat burns about two calories a day, contrary to what the myth states. So, muscle is three times more metabolically active at rest than fat, not 50 times.

Again, let’s use me as a guinea pig and do the math. The 20 pounds of muscle I’ve gained through years of hard work equate to an added 120 calories to my RMR. Not insignificant, but substantially less than 1,000. However, I also engaged in a lot of aerobic activity and dietary restriction to lose 50 pounds of fat, which means I also lost 100 calories per day of RMR. So, post-physical transformation, my net caloric burn is only 20 calories higher per day, earning me one-third of an Oreo cookie. Bummer.