I don't think the source of points is relevant in this case (ie they're not saying that if you pay for the ticket in points, that those points have to have originated from your MR account).
For example, say you want to buy a points plus pay reward ticket using Qantas points: you would pay for the ticket using points from your Qantas account, and use your Amex card to pay the cash component for the taxes etc.
See for example this article which is consistent with what I'm saying:
What’s included in your Amex credit card travel insurance coverage depends on the type of card you hold. Having complimentary credit card travel insurance comes in handy at such times by automatically providing a cover for your trips.
www.ratecity.com.au
"How can I activate my credit card travel insurance cover?
You’re generally required to book the full fare for a return trip on your Amex credit card or pay with the reward points earned on that card. However, some premium category cards may let you claim the insurance on trips booked with other reward points as long as you’ve used your Amex card to pay the taxes and other additional fees."