Confusing error message on Dockerfile context in triggers

Trying to set a build trigger on quay.io. I got the configuration wrong, but the error message is confusing:

Select Dockerfile:
/Dockerfile

Select Context:
/directory/

Dockerfile, /directory/, is not a child of the context, /Dockerfile.

The error message is not very clear, but most importantly, it looks backwards. It seems to imply that it considers "/directory/" to be the dockerfile, and "/Dockerfile" to be the context.