It means exactly that. It's not a good diagnostic symptom since (a) it may come on slowly and not be noticed as a change and (b) there are a huge number of things that could cause it. But if I noticed small mouth sores and then realized I had been feeling vaguely bad for weeks I would be more concerned about a vitamin deficiency than if only the first symptom were present. (Otherwise, well, maybe I have picked up a habit of biting my lips in my sleep.)

The symptoms of vitamin D deficiency I found are even less useful. Neither of the people I know who've had it had mentioned muscle weakness or twitching in particular, and you really want to find out you're deficient before your bones are breaking all the time. Luckily, unless you sunburn very easily, or have dark skin and live in a temperate or higher latitude, you can synthesize plenty of this one yourself without worrying about diet.