I... But... Why...Expansion: The reason why he's so quiet when you meet him on Mt. Shirogane is because Red has a gigantic mountain fetish. He's not stoic - you just disturbed him during his happy hour and now he's too embarrassed to talk.
In Black & White 2, he's still sexually frustrated and embarrassed by Gold/Hibiki outing his debauchery to the public, being banned from setting foot on mountains ever again, so he remains speechless.