Yea I've heard why. I just think it's strange. A hex key I can't imagine is a very difficult or critical piece to manufacture, it's a very common tool. What I would believe is being sent the wrong size. But did they really gather all their hex keys so last minute, that it would have significantly impacted their launch to order (standard sized) hex keys from a different source?
Like I said, I find the whole thing strange. Just seems like a last minute consideration to me. They were trying VERY hard to minimize their costs this time around, so I see that as a very likely possibility.
Sometimes it's just easier to take people at their word unless you have a reason not to trust them. I can't say I have ever had to source Allen wrenches before, especially in the UK. Do alot of manufacturers make them in the UK? They said they try to keep business local, so maybe that is making it harder? They have implied that they don't do business with China in one of the posts I read, and I'm sure it would be easier to source them there.
The thing is, you could probably straight up ask the owners for more details. They are responding to people's questions daily on their Facebook page. There is no reason to jump to our own conclusions. Who knows, they might even mail you one if you ask them. Personally, I like using Torx screwdrivers instead of Allen wrenches.