Sale of license – Accounting Standards

In the Sep/Dec 21 Q2.Agency Group question, part b asks us to discuss how the sale of the license should be accounted for.

I am a bit confused regarding what accounting standard to apply in that scenario. I applied ifrs 15 Revenue to the scenario ,treating it as licensing of property. However in the answer key they have derecognized the property and recognized a gain .

I think my answer would be incorrect as the transaction is a “sale of an intangible asset” and therefore would not fall under ifrs 15.
Can you tell me whether this is correct?

And I don’t understand why they have used both the standards to answer the question.Can someone provide an explanation.

thankyou