I know he didn't mean anything by it. I'm of an age where a lot of women do have children and my car does look like a pack of wolves invaded it.
However, it got me thinking that assumptions can be a really bad thing. I don't have children. I expect to have them eventually, but at this point in my life, mother's day is not a day I celebrate for myself. It's a day when I honor other people in my life.
What if I was unable to have children or had been trouble getting pregnant or had recently had a miscarriage or had a child who passed away? A phrase like "Happy Mother's Day" can be tossed out rather carelessly and with good intentions, but leave someone feeling wretched.