Did you hear them ask? Did they definitely ask him to make them lunch? Because I'm wondering if what they actually said, and he either misheard or understood, was something like 'Is there any way we can get a sandwich?' or 'Can we get sandwiches somewhere?' or something, meaning 'Is there a shop or a cafe near here?' rather than 'Can you make us some lunch?'
I've never had a builder ask me to make them lunch, but I've had plenty ask me if there's somewhere nearby they can get something to eat.
I actually always offer to make them sandwiches, because I'm probably making something for myself anyway and I really don't mind making a few extra, but it's certainly not expected and I've never been asked to!
Years ago we had plasterers in and they asked if there was a cafe or something nearby, and I said there was, but if they liked I could whip up some bacon and egg sandwiches instead, and they actually said that was the first time anyone had ever offered, so it's definitely not the norm!
Our last builder put us massively to shame by declining all offers of sandwiches and snacks on the grounds that he was a vegan who also shunned refined sugar or anything processed, and also did some sort of weird juice fast on alternate days. The only thing we were able to provide for him was oat milk for his one cup of decaf coffee each morning and a selection of herbal teas, which to be fair he was very grateful for. In fact, he gave us two tins of biscuits and a large box of very expensive chocolate truffles that he'd been given by his previous client.