@Valentin9 Under no circumstances should you cancel, except for using the My Host Needs to Cancel option as you would be subject to the host's cancellation policy and not be refunded the Airbnb service fee.
I have never heard of a listing having a minimum number of guests. Many listings have maximum number of guests, say up to 4, but that doesn't mean that 1 guest cannot reserve for 1.
I do see that the host has stated 2 persons, but I don't think that is binding. What is bindng is that your reservation has been confirmed and the host has to accommodate you at the price reserved or cancel.
If you want to double check directly with Airbnb, I would advise that you contact them through twitter @airbnbhelp. They respond rather quickly. Click on the link below to see other options for contacting Airbnb.
Please let me know what the resolution to this is. Thanks! Clare