I'm always fascinated by the 'you're just attention-seeking' comments.
What kind of attention did the OP want, exactly?
Public approval for her milk-producing skills? But why would she expect this when breast milk = piss, shit, blood, in the rationale of most 'you're attention-seeking' posters?
Public admiration of her body? Notwithstanding the fact that she wasn't even exposed, why does every physical gesture a female makes have to be construed as done for an audience? Every little action invites scrutiny, so if you don't run off to the toilet to pump then you must WANT people to look at you. You can't just, you know, want/need to express milk whilst continuing your conversation.
A lot of the comments here show that breastfeeding in public is not so much accepted as grudgingly tolerated: there's the baby, and it's obviously hungry, so yes I suppose you may feed him, although if you could swathe yourself in scarves or face the wall that would help. But producing milk without the baby? Revolting, showy, unacceptable.