The COC give DL the option of a rebook on the AC flight. As a practical matter, you need to ask or you need to luck out with an agent who looks. Here, the other pax either asked the agent with whom he dealt or the agent looked and offered it.

As a suggestion for future, it always pays to do the legwork yourself and to ask for what you want. The worst you can get is a "no".

In this case, OP is at least due a refund of the value of his EWR-YYZ segment. That may or may not cover his AC ticket, but it should be something.