What the rules are stating is that if you want to apply the discount code to somebody else's travel you MUST be the purchaser by using your credit card (or other applicable payment method). These same rules apply for the companion cert.

The "and" in the T&C is superfluous.

So, to sum it up:

Good:

You pay you fly.
You pay somebody else flies.
Somebody else pays you fly.

Bad:

Somebody else pays somebody else flies.