Not true at all. Many factors affect economic growth. Increasing population is NOT necessary for increasing economic growth. Look at Cuba. Population has grown since Castro took over. The Cuban economy has collapsed.
First, I never said there weren't many factors affecting economic growth. Second, your Cuban example is flawed. Cuba collapsed when Castro took over, and since it isn't a free market situation it can only grow as much as Castro's boot heel allows.
Besides which, you can have an increasing population without much economic growth, but it is nearly impossible to do much growing when your population is in severe decline.