I've been curious about that dragon line for a while as well. It really came off like Alphinaud was experiencing something Echo-like from the dragon communication, but he's not sure how to describe it, having never really experienced it before.
But at the same time, even you with your Echo hears the Dragonspeak as its own language, rather than the words being Echo-translated for you into "common" like with the Ascian language. What I mean by this is that we can understand Lahabrea, his voice acting is in our common language when he's speaking in his language (source: CS after killing Igeyorhm) and the dragons speak, even to you, in a language that's definitely not "common."
So basically the dragons seem really odd, again, like the Echo can be turned off in some situations.