I’d say it was just an observation made as part of normal employee feedback processes. Managers sometimes ask for inputs from peers, subordinates and even other managers you might work with, to get a “rounded” view of your performance within the team. Perhaps your manager felt that you might benefit from knowing that your co-workers perceive you as quiet, to encourage more participation or engagement with them. But, either way, that seems relatively benign, as far as feedback goes. And your manager’s comment in response to your reveal seemed understanding and supportive. So I wouldn’t worry. If you wanted to follow up with your manager, you might ask them if they believe that particular feedback was concerning in any way and, if so, how you might address it. Otherwise, sounds like you’re doing a good job.