Someone at the theater was burdened with a glorious purpose
Or they made a very odd mistake. The above photo is actually a fan's photo manip and is definitely not a scene from Thor: The Dark World (I think we would all have remembered that). Yet that image was the one chosen to promote the release of the film in a theater in China. Here's a comparison to the poster Marvel released:
To be fair, the actual poster is a little awkward.
Loki looks downright snuggly, while Jane looks ten kinds of ready to leave. Seems like a reasonable mistake to me!