That's an interesting one. I actually haven't read all the press, but whilst large companies will tend to want to minimise any comments on rumours, if the press kept repeating the story then it would get to a point where the BHP PR department would want to deny involvement if they are not involved.
From a market disclosure point of view they have no obligation as clearly not material to BHP share price.
Interesting that THX have not actually "announced" any denial of involvement - that I can see.
UMC Price at posting:
91.0¢ Sentiment: LT Buy Disclosure: Held