I think this description of poetic meters, with a notation that does not really correspond to how a line is pronounced, is confusing. It’s unfortunate they don’t make use of a more sophisticated prosodic theory. But most importantly, don’t they completely misrepresent the meter of Byron’s The Destruction of Sennacherib here? It’s perceptively an anapestic tetrameter; and they mark and talk of it as if it were an iambic hexameter.
(Also, as they inform the students, the terms masculine and feminine rhyme are "plainly sexist".)