Hi Eduardo,
Thank you for your questions.
I have not come across this terminology “Disposable Platform” in the cloud computing world. Good question, I don’t have an answer.

I would classify “Immutable Infrastructure” as: once you instantiate a version of the Infrastructure, you never change it.

While on the other hand, “Disposable Infrastructure” applies to pets versus cattle analogy to cloud computing from the twelve-factor apps.

Your Infrastructure is built such a way that you can quickly dispose of it, and create a new one if required. All is scripted, and nothing is built manually.