It is indeed kind of sad that some people seem to think you are a bot if you're not always chatty. I tend to talk with friends privately and / or watch some movie or series while skilling. This means I probably won't be chatting too much, if at all, with other people at the mining site.
I do hope you realise that not all silent skillers are bots. But if you really suspect someone of botting, you could always just report them, of course.