I was overpaid in 2020 (federal service worker). My debt letter said I only owed a portion of that overpayment. Is this too good to be true?

Back in 2020, I was mistakenly overpaid by the federal government (in the form of a student loan lump-sum payment). We’ll call this amount X. I opted to have this payment’s taxes taken out up front (we’ll call this withholding Y), so the amount that actually was paid toward my student loans was Z. Just so it’s clear, this checks out such that (X = Y + Z).

Now, halfway through 2021, I received a debt letter from the government saying that I was overpaid in the amount of X, but after “adjustments for payments and offsets”, the amount owed was actually only the amount of Y. So in other words, they were only looking to get back from me the amount withheld for taxes.

This seems too good to be true. My student loan account still shows my total loan amount reduced by Z, so it seems as though I was simply “given” Z and I only owed the amount of Y. This doesn’t seem right though, and I’m fearful that I will unexpectedly get another debt letter for Z at some unknown date in the future (or worse).

Can anyone offer any advice or their experience?