I think you sound completely normal!
I am more of the chatty type in my "non-work life" and in my CURRENT workplace...sometimes too much (although my supervisor says I'm fine). But in past jobs, I have been a lot more focused/quiet at work, and do like to work independently. So I can relate. I think some people just click in a way and have so much in common that they become friends. I can't speak for your coworkers, but I have plenty of work associates who don't really get that involved but as long as they are friendly and positive when I DO have reason to talk to them...my thoughts of them are really good, and I think they seem like great people! The only coworkers I don't really like are the ones who constantly stir up trouble or have a VERY negative attitude...it doesn't sound like that's you at all :-)
Your situation of working reduced hours with no lunch or breaks causing a decline in your workplace chatter really makes a lot of sense...I don't know how many hours you typically work, but it sounds almost like a part-time position and I think in most workplaces, part-timers seem to have almost an extra burden of seeming very busy and useful, kwim? I do work "regular" hours with breaks/lunch, and I have a lot in common with 3 other women and hang out with them outside of work, etc.
Also - it sounds like the nature of your work IS more independent...with no need to involve others constantly, so your supervisor probably approves of your strong work ethic and being so focused. I'm quality assurance, so the nature of my position requires me to know and deal with about 80% of our staff on a very regular (weekly or monthly) basis, so instead of being tied to one dept. I am my own mini-dept. and really need to be aware of what's going on everywhere in the office.
I honestly think if I worked in another dept. I would not be as talkative or "involved". I would probably limit my visiting a lot more. Like you, I don't feel comfortable interrupting others in their office just to chat. I take work pretty seriously. However, in my case there are always audits, reports, and other little (work-related) reasons for me to talk to people, so while I'm there I usually end up making small talk or discussing fun/personal things with employees too.
I really don't think you have anything to worry about as long as you're friendly and talkative when people approach you. It may sound weird but I do think it's important to keep up the hi/bye stuff with the employees who work closest to your office, I've seen that drop off between coworkers at times and it can seem tense and unnatural...even though sometimes the constant hello/goodbye seems unnatural too ;-)
Good luck sunny_days!