Videos are inherently large. There are better compression algorithms than what phone cameras generate by default, but video reencoding is slow, and the results still too large for "covert data channels".

Normal players would have noticed the bandwidth and CPU usage, and volunteers have already agreed to data sharing, so there's no point in keeping secrets. Same as claims that the Facebook app listens to people talk: someone would have caught it by now.

Also, AR capture was never very popular, mostly a gimmick for new players. The game was already a battery and power hog even without it.