> it's a sequence of instructions that either runs to completion atomically or doesn't

The way I read it, it either runs to completion in one go, or gets restarted from the beginning. This means the sequence as a whole isn't executed atomically, as the already-executed instructions during an interrupt aren't rolled back.

It can be used to build atomic actions, but it is up to the developer to create a sequence of instructions where the very last instruction "commits" the entire operation, with the side-effects of partial execution being harmless.