You are correct that this is what the article says - testing suggests it is in fact titanium, just maybe not the right treatment.

That would be harder, but one would think that a company making airframes for aviation, in a highly regulated environment/etc, would occasionally send off samples to double check them.

Getting titanium analyzed to a degree you could tell whether it is the right grade/alloy is cheap and fast - I can get it done for <$100 per sample.

Given the cost of what they are producing, how few they produce, and how much they sell them for, and how quickly you can get this kind of thing done, they could test every single lot of titanium they get and neither increase cost, nor slow down production.

This also isn't a case where there are lots of people in the middle - this supplier is the ones machining and producing the final product from titanium alloys.

Also, if you change suppliers, wouldn't you at least test the stuff they give you the first time?