When publishing social messages within HubSpot, you can mention other accounts by using the @ symbol. However, there is a setting within Twitter that categorizes messages that begin with the @ symbol differently. If you begin your message by mentioning another account, Twitter will categorize your tweet as a conversational message and it will appear on the Tweets & Replies tab in your account on Twitter. 

To avoid this going forward, place any character or word before the @ symbol. This will cause your message to appear on the Tweets tab as expected.

To learn more about creating social messages in HubSpot, check out this article.