This is a use-after-free, which should be impossible in safe Rust due to the borrow checker. The only way for this to happen would be incorrect unsafe code (still possible, but dramatically reduced code surface to worry about) or a compiler bug. To allocate heap space in safe Rust, you have to use types provided by the language like Box, Rc, Vec, etc. To free that space (in Rust terminology, dropping it by using drop() or letting it go out of scope) you must be the owner of it and there may be current borrows (i.e. no references may exist). Once the variable is droped, the variable is dead so accessing it is a compiler error, and the compiler/std handles freeing the memory.
There’s some extra semantics to some of that but that’s pretty much it. These kind of memory bugs are basically Rust’s raison d’etre - it’s been carefully designed to make most memory bugs impossible without using unsafe. If you’d like more information I’d be happy to provide!
Well they said .NET Framework, and I also wouldn’t be surprised if they more or less wrapped that up - .NET Framework specifically means the old implementation of the CLR, and it’s been pretty much superseded by an implementation just called .NET, formerly known as .NET Core (definitely not confusing at all, thanks Microsoft). .NET Framework was only written for Windows, hence the need for Mono/Xamarin on other platforms. In contrast, .NET is cross-platform by default.