This is a general question for guys...
Should a girl be worried if a guy just volunteers information to her without her asking?

Maybe... maybe not. You will most likely need to flesh out the story a little bit more with some information in order for anyone to give you an opinion on this.

For example if you just text hey during the day without anything else and then he responds with hey and then proceed to tell you what exactly he's doing, without you asking

Maybe he's trying to make conversation?

It depends on what he says he is doing -- grocery shopping or cooking spaghetti or using the bathroom.

I am so confused on what to think or assume sometimes

No big deal here.