I suspect the "too much emotion" is a misguided attempt to spin a negative into a positive. I think it's more accurate to say that autistic people have "more emotion than they can manage" -- trouble managing (or lack of instinct for how to manage) their emotions to express them in socially acceptable ways, so they either feel overwhelemed because they don't know how to express emotions effectively, leading to either "yelling silently" (which creates a feeling of isolation from people they want to connect with) or outburst that scare people away (leading to real isolation), or both.