On the full website, these types of routings are always fully highlighted indicating that they contain an airport transfer. I don't book flights on the mobile app, as I don't feel it gives you the same level of information that the website does. This is a perfect example of one of those data points.

While I feel for the OP, you always need to pay attention to the origin/destination airport codes. I know that IAD is not DCA, but then I travel a lot. There are a few airport clusters like that (IAD/DCA) (SFO/???/???) (LAX/???) that I know could result in a transfer if they are not my origin or final destination.

I agree that the mobile app needs to flag this kind of routing in a manner similar to the how the full website does, in order to make it very clear to the buyer that an airport transfer is included.