The CIA financed Signal (I believe they stopped a few years ago), however that was never really secret. It also happened in simpler times, in the earlier days of internet and mobile phones. In general it's quite plausible that the CIA just wanted a really secure comms system that people they wanted to undermine regimes could use.

Contrast this with how the FBI and the Australian feds bankrolled Anomphones, which they then used to read the communications of criminals. That was kept secret until they were ready to brag about it.