It seems reasonable enough that the government may have built a forked version of signal with message archiving that meets documentation requirements.

If its an app they wanted kept under wraps, it will make the while Hegseth situation seem a lot more benign.

I use Molly Messenger on a secondary phone that doesn't have a SIM, its a fork of Signal with a few differences related to encryption at rest. It still works with normal signal users just fine, on the other end you can't tell I have a different client. If the government has a similarly forked version you could likely still accidentally invite the wrong user in from their normal Signal app and they wouldn't know you're on a forked version with government archiving features.