One of the criterion for all work positions is potential for "engagement", or predicting your future buy in, vision, passion for your work, etc. This is not a casual concept: Gallup, for instance, reports that:
Companies with an average of 9.3 engaged employees for every actively
disengaged employee in 2010-2011 experienced 147% higher EPS [Earnings
Per Share] compared with their competition in 2011-2012.
with an average of 2.6 engaged employees for every actively disengaged
employee, in contrast, experienced 2% lower EPS compared with their
competition during that same time period.
So actually, if you aren't engaged with your work and think it is individually important in it's own right, you are a potential liability to the business.
The interviewer, in their undeniably imperfect way, is trying to divine the future and your potential engagement, motivation, etc. That's what they were looking for with the question - it was an invitation to try to convince them you care about the job, are confident in your ability, and feel you have something worthwhile to offer.
With the idea of "making a difference", they are trying to also divine your potential for POBs - positive organizational behaviors - which are in some cases positively correlated in research with lots of "good things" like being absent less, being more productive, job satisfaction, etc.
As for making a difference to such a large company, you are thinking too dramatically - if you have nothing to offer that would make a difference, then there would be no reason to hire you. If none of us made a difference, there'd be no reason to be alive at all - depressing, isn't it? But just because you don't think yourself the next Einstein doesn't mean you don't have plenty to offer, and none of us must become a peer of Nelson Mandela just to "make a difference". They don't expect you to revolutionize the company, just make a contribution - which would have been a better way to phrase the question, perhaps!
Also, technically you can always make a difference to even the largest company - you can always burn their HQ to the ground. They are trying to avoid that kind of employee as much - or often much more - than they are looking for a good employee. Every question is a way to get you out of being seen as a potential horror story, just as much as it's trying to see if you'd be a really good hire.
Again though, all of these questions are invitations to talk about your greatest skills, accomplishments, work ethics, etc. So if you get a lofty flowery question like this and you don't know how to answer it precisely, just correct it in your head to "So, tell me about your greatest workplace strengths...", and they'll often get the answer they were looking for anyway.