Multithreading is something that you have to plan from the very start of a project, and if you want to implement it in an already existing program it will be excruciatingly painful for all but the best built programs and the smartest programmers.
I assume that you'd not like me to rehash why that statement is not necessarily true. That's a very general view of multithreading and may be the case here, but we cannot know since we cannot evaluate the source.
That he says it would be difficult may make it difficult for him, but it does not make the task itself universally difficult.
That's actually not what I said. I didn't specify for whom it was difficult. What I mean is that just because someone says something will be hard (for them), does not mean it will be hard (for them). Maybe it will, maybe it wont. Programmers often get intimidated by the concept of threading, but threading isn't always complex and oftentimes can be completely abstracted. Has it been attempted? No idea. I assume he's done some work, but perhaps the angle of approach is wrong. Or perhaps he was using the wrong tool. You can mow a lawn with a weedwacker, but it will be difficult (for you). If you use a mower, it'll be less difficult (for you).
Just an example.