Why is 11-oxabicyclo(4.4.1)undeca-1,3,5,7,9-pentaene aromatic?
The aromatic system should be planar. The oxygen is not part of the aromatic system.
Please note, of course, that your drawing does not capture the 3-dimensional geometry of the system. You would still have to analyze the carbon skeleton to see if it satisfied the planarity constraint enough to be aromatic.