You're basically correct. Everything in Rust is value-typed by default. A Box<> puts a value type on the heap (makes it a reference type). The difference from a normal reference type is that a Box is owned (in Rust ownership terms), where other references aren't. Both normal references and boxes can be typed as dyn Trait which means they dynamic-dispatch method calls based on some trait, instead of statically dispatching them to the concrete type.
Funny that he answered that so early on, my line of thought coming from C# was "Are they trying to turn a value type into a reference type? I thought Rust doesn't have quite the same distinction so is this some weird way of working with the heap instead of the stack?"