This doesn't feel like a helpful response. I understand that pixelfed is federated, but I still knew exactly what the commenter meant when they said they poste

This doesn't feel like a helpful response. I understand that pixelfed is federated, but I still knew exactly what the commenter meant when they said they posted "on pixelfed". They meant they posted on an instance running the pixelfed software. It seems like it was effective communication to me, and your correction seems both dismissive and unhelpful.