It is not guaranteed that the survey you have received is anonymous.
If it is, it is usually indicated in the text of the invitation.
Nowadays, it is common for surveys targeting employees to have support for protecting the individual's responses, but it is less common for customer surveys or market research surveys.
If the survey states that you can respond anonymously, Quicksearch has a lot of functionality in place to protect your data so that you can safely respond without your answers being disclosed.