The idea that any "internal communication" will remain as such in the modern era is laughable and everyone (including those writing them) knows that.
Many companies use "internal memos" as a way of getting news out there without officially releasing it, as it always appears to be a more trusted source than were it to be released directly.
No idea if that was the case here, but the thing I often look for is who would news like that be aimed at? What is the real reason for making statements like that?
There's always a game going on somewhere and statements like this are just part of it.
Will Monarch get 787's? No idea, but it's a risky strategy committing to aircraft that are that expensive, especially when they're already in the process of bringing one new type in.