Looks to me they duct is not square/parallel to the steps,
and unless you expected the tiler to reposition the duct, which I expect he did not fit and cement in before hand,
I think if he laid the tiles parallel to the steps he/she would have to cut the tiles off square around the duct which would be very noticeable
going up and down the steps or worse looking out at the patio,
in other words the way it is tiled is the best of both worlds (not as noticeable off square under the steps,
And possibly took longer to lay than if they cut them off square at ducting,
In other words the problem in with the person who installed the duct off square to the steps and whoever signed off on it,
if you want everything square reposition the duct and pay to replace the tiles
it was a catch 22 situation for the person laying them,
I would say most would not take the time and effort to lay them as is,
did the contractor who put the duct in place hire the person who laded the tiles for you,