We don't actually know that. What we know is that they said they didn't share anything intentionally. But there is almost no penalty for lying about such things and the USPS is desperate for money, so I don't think it's impossible that some USPS person made an under-the-table deal with Meta or another company to add this stuff to its website in exchange for a kickback. Only a detailed audit would be able to find out the truth, and that seems unlikely to happen unless Congress gets upset about the issue.