What do I make of the metrics?

By themselves, nothing. But I am (and was) arguing that they are useful as clues that can lead to profitable conclusions.

I would also (and have, recently) argue against the idea that they should serve as commentary on code quality, or heaven forbid, "quality gates" for code review.

So, if they can't be used in isolation, why have them?

I routinely deal with large amounts of source code, and most of it is the product of many many unique minds over many years, combined with an endless treadmill of maintenance and tweaking. Apart from asking the individuals with the knowledge - who have often left the company by this stage - what else can I use to help focus my (our) attention for code review, unit testing, and so on.

Obviously, I can also find clues in reported problems, but isn't that just another metric?