British uncle thought I'd been talking about needing pregnancy underwear all week

For context I'm Canadian and my uncle is British. I saw him regularly for a week while he was visiting with my aunt for a family event. My jeans had just stopped fitting, so throughout the week I mentioned that I needed to go out and search for some bigger pants, if anyone had recommendations for where to buy maternity pants locally, etc.

When I came back with my purchases he was like 'OHHH you were talking about trousers?! I thought you had been talking about needing maternity underwear all week!' LOL I guess in England 'pants' is the word for underwear.

PS: This made me flashback to when I was 8 and my Australian friend told me that 'her family keeps their thongs in the closet' (thongs = flip flops in Australia).