According to Bloomberg Apple and AWS had already investigated thoroughly, had talked to the government, and their executives were the ones who had leaked to Bloomberg in the first place.

Published along the initial story were strong refutations from Apple, Amazon, Super Micro and Chinese Goverment. Some of them suggested that this is not the fist request from Bloomberg, so much that companies got annoyed to refute baseless speculations (see Apple response). So Bloomberg consulted with the companies and published despite the strong denials from all sides.

They did. Apple said they did 3 separate times, and in all times found absolutely nothing. Bloomberg chose to publish the story anyway.