See that's where they differed. Susan was a very social creature, she adored being around people and talking about anything and everything. She also tended to speak at the rate of knots when she was particularly happy or excited about something and she had to consciously slow herself down, but that just reminded her once again that her powers were on lockdown.
So he could speak, imagine that. Though judging by the sound of his voice he found it difficult so maybe that's why he wasn't as forthcoming as others were with their speech.
"Welcome," Susan offered as she waited for him to take some before she popped a further one into her mouth.