Indeed, it appears that you've called him (according to screenshots), but maybe it was a wrong tap, because I can't explain how that happened. Sometimes I mistakenly tap on different areas of the phone while I am in an application of this kind and start a video chat. The most interesting part is that it doesn't appear in your chat log. Every action is displayed in the chat log if it's a video call, voice call, or regular chat messages.
Make sure to change the password for your Viber account and re-register to avoid any other complications.