Signal development came from an ex-Twitter director that was initially sponsored by the CIA (through Radio Free Europe) and then developed with experts on the backyard of the NSA (Hawaii). Eventually this relatively unknown messenger algorithm got adopted by a messenger company own by Facebook (a privacy loving group) for over a billion users.
It ain't no surprise that just about everyone relevant in the crypto world prefers telegram than something called "signal" (just inform yourself what it means in the intelligence community).