"dorian is amajorscale with flat 3and flat 7"

This is at best misleading. A person setting out to teach something should be able to come up with an unambiguous explanation of the concept in question. What we got was an unclear account. On that basis, I am with Mark.

Dorian is not, as the quotation appears to state, a major mode. It is seen as a minor mode because the third is minor (ie flat 3).

It might have been more helpful to state that you make a major scale into a dorian one by lowering the third and seventh notes by a semitone each.