If you have enabled Profiles for your meeting, participants will be prompted to enter their details when they first join your meeting. They can add a First Name and/or Last Name.
They can edit their profile at any stage and remember... they can enter anything as their profile that they want to.
For a meeting where you want participants to be truly anonymous, then you can turn profiles off. This is done when you create the meeting or at any stage afterwards by editing it from the meetings list. With Profiles off, participants will appear as 'Anonymous' in the dashboard and in the meeting report. The message board will show no profile text and your participants won't have the ability to go their profile in the app.