This seems to be why he said it. He was signalling in to a certain demographic that he's for them.
Asked if Starmer felt the laughter was evidence of snobbishness towards his father, he replied: "I don’t know what caused someone to laugh, but if you're laughing at someone because they work in a factory - that is the one thing that I think had a massive impact on someone like my dad, the disrespect. And it’s in me. You can see I'm angry about it, I am frustrated, because I will never allow that sort of disrespect for working people to be any part of my plans, any part of the Britain that I want as the future.”