I've just read the Apple letter to the congressional Committee on Commerce, Science and Transportation (bd139 has the link above).
I've read a lot of "non-denial denials" over the years, and I think I know how to spot one now. The Apple letter has none of the characteristics of a "non-denial denial", it lacks the over-specific denials, weasel words or tone that characterises them. It sounds like a honest denial that should be taken at face value.
Although this whole issue is still in a fog, it's increasingly looking like the Bloomberg story is a pile of steaming manure.
Bloomberg have a reputation to maintain - ultimately in the serious news business it's all you have. So it is not in Bloomberg's interests to create a 9 days wonder story in the way a piece-of-arsewipe tabloid might to sell a few extra copies - "Major IT Suppliers Compromised by Spies" is not "Kim Kardashian's Cosmetic Surgeon Says Left Buttock is Fake". You can bet that with a story of this significance and apparent long research time, that layers of Bloomberg's management and lawyers would have been over the story before it got the green light to publish. So I think we can discount that Bloomberg deliberately created a fake story out of thin air.
So if we accept Apple's denials and (tentatively?) those of the other named parties and discount the possibility that Bloomberg deliberately fabricated this, that just leaves malicious action on the part of a third party in planting the story with Bloomberg. Claims that some shadowy US government department or the US political apparatus ordered Bloomberg to publish this are not credible. Bloomberg has both good enough lawyers and enough ability to expose such a thing publicly by publishing, that it would be both legally and politically unthinkable. That just leaves an organisation with enough manpower and experience to run an operation designed to get Bloomberg to believe the story - which surely means the intelligence/espionage apparatus of some state level actor or similar. If we accept that, the next question has to be the old one, cui bono, who benefits?
Answering that question takes us down the rabbit hole of conspiracy theory. Not the Chinese, obviously. The French? I wouldn't put it past them, just for spite. The British? No real benefit to them. The "deep state" or someone trying to implicate the "deep state"? The illuminati? The tri-lateral commission? Scientology? Like I said, rabbit hole.
Realistic answers might include: Russia - detracts from the various investigations into their interference into US politics, plus they hate China. Domestic political groups - stir up righteous patriotic fervour with mid-terms coming (against: maybe rather too competent an operation for political rabble rousing). Israel - again, mid-terms, electing right wing pro-israeli candidates might make a little sense but not very much, but the Israelis have demonstrated in the past that they are prepared to do stupidly destructive things to gain a little advantage for themselves so it's not completely beyond reason. Any other sensibly plausible actors?
Edited to add: I'm dismissing straight cock-up theory because of the huge number of sources and the layers of approval that (at least in theory) this ought to have gone through at Bloomberg. If I'm wrong, then the level of journalistic competence shown is less than I could manage if I was simultaneously the most drunk I have ever been, with both hands tied behind my back, with an eyepatch on and just after someone's shot me in the left leg.