I would take your thought a step further and suggest that it was not even an invitation to dance, rather than an invitation that Darcy was certain Lizzy would turn down.

The comment did not come in the conventional form of an invitation to dance, and there is some question about whether there were enough people available for a reel, and whether, even if he actually did like that type of music, the reel is the type of dance the dignified Darcy would have chosen.