This is either the mandela effect (I know for a fact that the server was stuck on "April 2020" for at least 6 months), or Signal intentionally hid development and then revealed it all when they realized it was bad PR.
I saw that not too long ago myself. Purely speculation here, but perhaps they opted not to publish any commits until they had a chance to have their MobileCoin implementation audited? Just wish they had been more forthcoming about why they were not pushing commits.