That is simply wrong. Rust makes it easy and safe to share immutable data – it's the ability to mutate that can't be shared.
> data is owned explicitly and passed explicitly
Yes, data is owned explicitly, but the permission to read or write the data is somewhat independent of ownership – the owner of an object can grant permission to access the object, and it can pass this permission to other threads without relinquishing ownership.
> it's the ability to mutate that can't be shared.
So, I do think you're more right than your parent, but I also think this formulation misses important things.
Rust only lets you share when you cannot cause a data race. A type like Mutex lets you share something that's mutable, because the mutex is guarding the sharing. Functions like split_at_mut let you mutably share disjoint parts of a slice.
That is simply wrong. Rust makes it easy and safe to share immutable data – it's the ability to mutate that can't be shared.
> data is owned explicitly and passed explicitly
Yes, data is owned explicitly, but the permission to read or write the data is somewhat independent of ownership – the owner of an object can grant permission to access the object, and it can pass this permission to other threads without relinquishing ownership.