1. If the “advanced” civilization is attempting to communicate with previously unknown civilizations using radio energy, the radio frequencies to be used are rather obvious due to the limitations of using other radio frequencies, and encryption of the radio communications would be obviously contrary to the purpose of making First Contact using such primitive technology.
Snowden's talking about routine communications being intercepted by distant civilizations, not about deliberate attempts by one civilization to contact others which may be somewhere "out there". His argument is that such ordinary traffic, if receivable at all, would be indistinguishable from noise, due to routine encryption employed by civilizations advanced beyond a certain level.
I already addressed that scenario in Point Number 2. Interstellar distances are too great for radio communications to be useful in ordinary communications, because such radio transmissions take to many years, centuries, and millennia to transit the intervening space and require too much transmission power to be detectable at such interstellar distances. Unless an alien civilization just happened to be located within only 1,000 light years of the Earth and was radiating their radio emissions within 1,000 years ago, we simply could not detect their radio transmissions. About all they could say to each other would be to indicate the colonies in their other solar systems were still around when the message was sent and communicate other stale information and requests. Without what effectively amounts to some form of Faster-Than-Light (FTL) transport and/or communications, the feasibility and utility of interstellar radio communications is very limited in purpose and range of distance. Whether or not such inter-species communication were taking place with encrypted radio traffic, it would not matter to us because such transmissions would be undetectable here on the Earth.
“His argument is that such ordinary traffic, if receivable at all, would be indistinguishable from noise....”
No, because the carrier signal would be detectable whether or not the message was encrypted.