Colin is correct.
I called my mate and asked (Couldn't stand not knowing).
After a check of the MX Manuals and Tech supplements for ADR's, etc, the findings are....
CAS (IAS for all intents and purposes) from ADR 1 or 3 below 280 kts, move the gear handle down, and you get....Noise!
The gear will go down irrespective of altitude.
(Above quoted from an Airbus Employed, A330 Technical Services Manager)
Which certainly explains why
There is nowhere anything written that the max altitude of 21000' blocks the operation of the gear
I learned something new today.
Now it's time for those drinks....
Cheers