It was misleading of Bishop to bring up pensions in your linked politifact article[1]
Take the case where every company in the USA (including the post office) is required to do X and Y, but only the USPS is required to do Z. It's a true statement to say that "only the post office has to do Z". It's also a true statement to say "Only the post office has to do all 3 of X, Y, and Z". But the latter statement is abusing boolean logic to make it sound like X and Y only apply to the post office.
[1]: It's also misleading to say they "must fund 100% of the costs in advance" when the actual requirement is that the pension plan be "fully funded". If you're fully funding your pension plan, compound interest is probably covering at least 50% of the costs.
Per this, your statement isn't fully correct either, since the new rulings made the USPS an outlier.