This is my guess (though not necessarily correct). The search only looks through the text of the messages. The name of the person who created the post is not always in the message itself. If someone responded to you by name, or quoted from one of your messages, then the text "Tracy_Lit5" would appear in one of the messages, so it would be found in a search.
The way to find all topics created by someone is to click on their name, which gives the number of topics they have created, then click on that and get a list of the topics.