If they did, I'm sure that OP or you can find a source for this statement. A rumor published by Bloomberg (or, in a more charitable interpretation, an estimate given on background) is not "publicly stated".
This is false. The link goes to a Mark Gurman article in Bloomberg that claims Apple at one point had an internal prediction of 3 million, and that it was revised down before it went on sale. That may or may not be accurate reporting, but it’s not close to claiming they publicly predicted 3M sales.
For everything I’ve seen of the Vision Pro it has represented a solution in search of a problem.
But I'm sure the cost of components ate a ton of that, and I'm not sure how much of that would be fixed vs. marginal costs. For something like the custom silicon, I could imagine fixed costs were substantial compared to marginal costs. I'm also not sure how much of this can be amortized across future versions of the Vision Pro, or if a huge amount of the fixed costs will need to be repeated.
Maybe for the amount of silicon fabrication tooling, and the complexity of manufacturing tooling for something so unique, the fixed costs required the sale of 2-3 million units to break even. If so, I could see various parts of the organization feeling pressured to deliver analysis which confirmed the necessary level of demand, especially if executives expressed bullishness on the project.