look this pic published in one online news paper

Yes, the restaurant is from the Maoist heartland. They are known to run such "sajha", "sahakari" etc "hotels" in their strongholds, and beef is a regular feature of their menu. I also remember reading reports stating that villagers were often forcefully fed beef by the Maoists.

To my understanding, cow slaughter is prohibited in Nepal but consumption of beef is not. For the very reason, beef, legally imported from India and possibly elsewhere, is commonly served in restaurants in tourist areas such as Thamel and Lakeside, Pokhara.