You'd be astonished how many junior developers come into industry knowing nothing more than their technical brilliance (and they
may be truly technically brilliant) and thinking they know everything. The fact is when you're starting out, as brilliant as you may be, you have little more than your technical brilliance. 5 years from now, this same junior developer will realize he doesn't know everything and will have a greater respect for everyone he works with... except his juniors who he will probably perceive as thinking they know everything.
Everything is new, but everything is old. And around and around it goes. The funny thing about history is that as much as we move forward, so much of our reality is just a repeating pattern of the past.
Nobody knows anything and we're all just making it up as we go along. For my wealth of knowledge and experience, which is considerable, there is still so much I don't know. There's still so much you don't know and there's still so much this junior developer doesn't know. But we all have something to teach and something to learn. History has shown though that the more junior you are, the less likely you are to be aware of how much you don't know and the bravado of youth is still very much in play. There's a reason the phrase "I wish I was still young enough to know everything" was coined.
Of course, it doesn't help to tarnish everyone with the same brush. There are those who bring genuine insight, but they are so few that it's a shock when they do. It's not unheard of, but I'd be surprised if this junior programmer has any clue what goes on in the heads of his colleagues and is projecting their thoughts based on a complete lack of awareness of a much larger context in their heads than in his own.
Communication is the key to resolving this issue. Nothing more.