Kind of curious, but have you tried to change your major topic? Or did you really just settle,"Okay, I'll tweet about React". Did you encounter that feeling of "I want to talk about many things"?
I'd say my one topic is actually: "teaching web developers". I happen to talk a lot about React, but I also talk about JS in general, and Rails sometimes too.
That seems to be fine - your topic CAN be something very specific like "React performance improvements", and you'll do well, or it can be something like "How to be a more effective web developer", and that will be ok too - just don't switch between topics like web development, then cooking, then politics, then your dog, then a little more web development, etc.
Sharing some of your life (like your dog, hobbies, etc) is good and is part of you being a "real person", as long as say, 90% of your content follows your major topic.