Thanks, FD, that's an interesting (tho' slightly different) point. It's one to be careful of, because one has to watch the words. We recently bought some new aircraft, the manufacturer's tech manual of which had similar words. When we went back to them and asked "So can it distinguish a true from a false GP?" the answer was "Oh no, that's the responsibility of the crew. We mean that the equipment is capable of intercepting a GP signal from above".
The 737 may be different, but I'd suggest it's worth checking.