If it seems weird to you, it's just because JAMES CALLIS IS WEIRD*. He's not like Tricia Helfer; he won't tweet straightfoward observations about his day. He will quote song lyrics, say cryptic things that may be impossible to decipher, and tell goofy schoolboy jokes. Also, he abuses dashes, doesn't always type things right, and over-capitalizes. I dunno what's up with that, but it's adorable.
If you want a sample of his style, read his messages to fans from before. Totally consistent with what he writes on Twitter.
James is a laid back, casual guy. He can be funny and silly or heartfelt and shocked at tragic world events. He's fun to follow. Just don't expect a rock star.
* and I mean that in the very nicest possible way