Why would it? Cargo Cutlting is when you believe that doing something symbolic will have a tangible effect on the world (e.g. bring you cargo from the sky), but this is just intended to be symbolic.

I was curious, and you’re right. It would be Cargo Culting then, if we believed the ritual actually had an effect on Pratchett in the afterlife.

Surely not. That's just most religions.

Cargo cults are quite specifically believing that the incantations have an effect in this world.

"The first documented cargo cults were religious movements that foretold followers would imminently receive an abundance of (often Western) food and goods (the "cargo") brought by their ancestors."

https://en.wikipedia.org/wiki/Cargo_cult