Obviously, it will always be multiple things altogether.
If we're talking about growth in terms of business, then it will obviously be trading volume(hence fee revenue).
I will never believe in such reports as CEX in the past are know to use bots to increase volume.
What's wrong with bots? Traders use bots to automate trading processes all the time.
If you're referring to these exchanges using bots to fake volume, then that's another thing.