When you navigate a Q2A site you're given a "key" that is stored in the browser you're using and can be identified by the server. As long as that key exists in the client (browser) and in the server a match can be made between them. If any of them lose that key then the server will assume it is a new user and give them a new key.
You have asked this question as an anonymous user. That means the question is actually associated to your key on the browser you're using. If you use the same browser to see this question, and still have that key, then Q2A will match you as the asker and you, and only you, will be able to select the answer to the question. If you use a different browser, or you clear your cookies, then you won't be able to operate on the question anymore.