I understand where you are coming from; indeed it makes me smile a little how well I can imagine both the scenario you describe, and your reaction to it. I can understand this in large part because I have Asperger's syndrome, a form of autism. Johns-305 above mentions Data, a character who is often loved by people who are on the autistic spectrum because, though he is an android, his behaviour, and especially his incapacity to understand or emulate certain kinds of human interaction, overlaps somewhat with the way that autistic people operate among neurotypicals ie. those who are not autistic. A similar joke to the one you describe is also made in the TV show The Big Bang Theory where the friends of Sheldon Cooper, a character who is sometimes said to have Asperger's syndrome, joke that he may be a robot.
People who are on the autistic spectrum differ from those who are not in a number of ways. Some of these relate to physicality: people 'on the spectrum' often have an idiosyncratic gait, a way of walking and holding themselves. Often we are said to be more logically-focused, and more literal in our thinking. We are typically not intuitive in our understanding of social situations and can often have problems reading peoples' moods and intentions: very often people do not explicitly say what they think, but suggest it somehow; typically we miss this and interpret only the actual words they say. What may be most relevant to your reaction to the situation you describe is the fact that it does not appear to be perturbing to you but in the notion that it is a waste of time. I have worked in a variety of situations, places, and contexts, in a handful of countries. In none of them did people go to work only to do their job. My guess (and I admit it has often been either galling or challenging for me), is that people in the countries and contexts and workplaces I know (education, hotel & catering, retail) spend 10 to 40 per cent of their time chatting and engaging in social activity not directly relevant to their task. This is about morale, yes, but even that makes it sound rather more pragmatic and goal-based than this tends to be in most work environments I know. People like to chat. To get on well with them people like me have to figure out a few ways to play along with this, even to find a handful of reliable subjects we can enjoy talking about with out colleagues (film, music, television, sport etc).
None of the above should be regarded as anything like a diagnosis (it couldn't be), nor necessarily a suggestion that you may or must be Aspergic. The scenario, however, is familiar to those who have Asperger's syndrome and both the way your colleagues react to you and the way you react to them would likely be understood by people who are 'on the spectrum'. This aside, my advice, if you really are not upset by their comments, and if you are reasonably sure they mean it kindly, would be to find a way to see it as their way of reaching you socially when you are so obviously focused on your work, and perhaps finding a way to understand that for most, chatting and passing the time socially at work is far from a waste of time. It is equally possible some of them may be being mean. If so, they only 'win' if you allow it to bother you.
ps. people on the spectrum, like Sheldon Cooper is sometimes said to be, are frequently highly gifted in their field. Paul Dirac is one example of somebody in the real world who had, to say the least, a fair handful of autistic traits.