Only if you stretch that definition beyond what most people are comfortable doing. The org includes the entire Bing team, for example. This would be like Google saying they have an x,xxx big AI team because they include the whole Search org, or the Apps org because they use ML in their products, too, and so do the Maps Mobile team, etc ad infinitum.
It's great that MS is merging these dispersed orgs, and the actual headline is fine, but calling it a "5,000 person AI division" is disingenuous at best.