I'm sure that hangglider pilots use checklists too (a flow-type memorized checklist is a valid checklist, just as a written one). I believe he used the wrong one (the no-passenger "solo" memorized checklist) in this case.
I would be more curious about the circumstances (e.g. rush before takeoff, stress factors, tandem-flying experience of the pilot in this particular case, why didn't he ask someone to check the passenger's gear, etc..) that make pilots fail executing the checklists (even the written ones) or to use the wrong one.