Living on a fixed income

I have taken on a second job working in a call center for a major retailer in the area to score a few extra bucks around the holidays.
I got a call the other night from a woman looking to purchase a pair of slippers for her husband. Not to judge, but you could hear the years in her voice. In the normal progression of the call, I asked "And may I have the number of your next item?" She replied, "Oh no dear that will be all, we live on a fixed income". After having gone through Financial Peace University, I said "I can completely understand!" She probed a little further and said "Well, how old are you?" I said "In my early 30's"...she had no need to know that I am, indeed, not quite that old. Quite indignant, she replied "So how many kids do you have?" And I politely replied "2 of the 4-legged variety." She scoffed. "You don't know anything about living on a fixed income."
Like an infected splinter, this has bothered me.
No, I do not receive my paycheck from the government on a monthly basis.
Yes, right now I work 2 full time jobs, and my husband is salaried.
We have no credit cards.
We are paying back student loans.
So how is this not considered a "fixed" income? I work the same hours pretty much every week. And I am not allowed overtime.
There is a finite amount of money coming in, and yes, it currently pays the bills.
And just because I don't have kids, that doesn't mean I don't know what it is like to live on a "Fixed Income". We are on a budget. All of our money is spent on paper ON PURPOSE. EVERY MONTH.
So how can someone sit and say "WAH!" you don't know what it's like!