^^^ I tried Googling the Mark 2Z marking, which turns out to be a British military designation. According to the
Imperial War Museums, the Mark 2Z cartridge came about when the earlier Mark 1Z cartridge was found insufficiently powerful to cycle Sten guns reliably, causing some (presumably exciting) full-auto mag-dumping runaways when the bolt did not travel far enough back to reengage the sear.
The Brits upped the power and called it the Mark 2Z.
Remaining stocks of Mark 1Z were reportedly marked "Pistol Use Only" and the cartridge was officially deemed obsolete in June of 1957. One would assume that the Mark 2Z cartridge must have necessarily been used in pistols from this point forward, although the link does not positively say that.
This site says that Mark 2Z achieved NATO standardization in 1962, with subsequent boxes being marked with the NATO cross-in-a-circle marking, but the ammo on the CIA website doesn't appear to be so marked.
Reports from various online forums—notably Aussie and Pakistani sites—suggest that Mark 2Z is loaded pretty warm. That said, some shooters have obviously been using it in pistols without catastrophic results, at least not immediately.
Bottom line: I can't find any formal-looking guidance positively stating that it's safe for use in pistols. The statement on the CIA website may ultimately by CYA, but I can understand why it's there, as it sounds like this stuff is the equivalent of a hot NATO or +P+ load. I personally wouldn't risk it.