What does this even mean? Be specific in what Sony did that Epic needed help with.
it means they helped them with the engine not necessarily the demo
the engine is an application to develop games it can cross compile to other systems like consoles and OS such as windows, linux, Mac, Andoird, Ios
the demo is a small game made in the engine and compiled on it to run in certain system, in this case PS5
sony helped Epic with the engine to ensure it uses PS5 correctly because different systems work differently so certain function has to be adapted in some way for a particular system and in another way for another system, the demo was made by someone inside epic using assets and sound from other people(maybe from Epic too) and scripts(or c++) using unreal API(that internally adapts to PS5 API) it may o may not have direction from sony(I dont think that is the case)
sony made the machine, have an OS for it they made the low level API, compilers, how the os works, the security system, best practices and plenty of stuff, its normal that developers ask to the hardware developers for doubts and opinion there are also forums for developers, and there are feedback, sometimes the hardware developer can also send engineers to help with the project and Unreal Engine is a big project that is included in sony SDK that requires special permission to be used and communicate with the system
MS and Nintendo also do that