It's also possible that they're using an alloy which is not easily detected, or that the titanium is in a part which was painted or otherwise coated before receipt by Spirit
Seems implausible. Again, Ti is way out on the edge of properties, being intermediate between steel and aluminum in weight and stiffer than either. That alloy would be a pretty novel thing, and novel metallurgy is more expensive than the hot Titanium someone stole from a bomber graveyard in Siberia.
Titanium isn't stiffer than steel. It's around half as stiff. It is also about half as dense, so the strength-for-weight is somewhat better. But you need more of it to achieve the same strength.
Outside of medical usage I think most commercial use of "titanium" is actually titanium alloys.
I'm sure I read somewhere there's over 50 commercial grades so substituting one for another close but cheaper grade with forged paperwork is very plausible.
