What’s the proper setup for mounting a tile cutting blade on a grinder?
13,000 rpm blades are fine. While centrifugal force does mount quickly as rpm increases, 3,000 is adequate headroom. The concern is that the blade's mass tears it apart at maximum tool rpm. 

The key to reasonable safety is making sure that the blade is both centered on the arbor and secured to the motor. If your blade arbor closely matches the arbor diameter, and you can securely sandwich it using the supplied nut along with washers of almost any kind, there's not really a problem using the tool like this. If you feel any wobble or imbalance, evaluate the situation before proceeding.

I've used the same AvantiPRO Turbo blade in my 7" grinder to cut hundreds of concrete pavers with great results.