Although this isn't super clear, it usually means that the viewers have come directly from another channel's page. While this is typically a host, auto-host or raid, it could also mean they just clicked on your channel while viewing the other, or they clicked on the sidebar. Views from Outside Twitch
You can click on any clip to view it. Where did my views come from? - This shows the total number of views and the source of those views. Your views come from Twitch pages and products (e.g. Followers, Browse Page), channels on Twitch, and external sources. You can click View Details to see even more referrals data.