Veggie or meat?

Today, I went to an air-conditioned foodcourt at Pioneer Mall to buy my dinner. The signboard wrote "2 veggie and 1 meat $3.20". As someone who don't eat veggie, i picked potato (a harshbrown) as the substitute for veggie. At payment time, i was told that the packet of food cost $3.80. I asked why and they informed me that potato is considered as a meat. Why is that so? So weird. All other stalls I've went to (in foodcourts) considered potato as veggie. It's so embarrassing when the stall lady told me loudly (and there was a long queue): "Xiao Jie, we always charge the potato same price as the meat". (And I was not complaining, was just politely asking why it's $3.80 and not $3.20) I think she could be more polite by excluding the "Xiao Jie" from her statement, as it sounds very sarcastic under her voice tone.