it say “he Hub contains a ZigBee radio (2.4 GHz) and a Z-Wave radio (900 MHz). These allow the Hub to communicate with your ZigBee and Z-Wave devices.”
All of that said, the Z wave frequency assigned to Saudi Arabia is 868.4, the same as Europe/UK.
Different regions have different frequencies because the local frequency used for mobile phones and emergency services communications like ambulances vary.
In some countries, it is illegal to use devices on the Z wave frequency of another region because they can cause interference with local emergency services.
So you should definitely check to make sure that it is legal for you to be operating without a license on the US frequency before purchasing any more equipment.