Hungry customer being refused to eat at the restaurant

Good day I write this review with disappointment in my heart as Macdonald's is a favorite place for my kids and I. On Wednesday 15/03/23 I went for my medical check up in Vanderbjlpark afterwards I decided to go to Macdonald's as normally do. Then my daughter called me and reminded me about Steers Wacky Wednesday special okay I then decided to go to steers for the special then headed to Mac D, I dnt like steers chips I enjoy the ones from Macdonald's. I went the and ordered Mc fries and Fizzy passion fruit juice, upon paying I then asked the cashier if it's okay if I have a burger from steers and eat with the chips 🍟 I ordered with juice here in the restaurant. The lady said no you are not allowed then she asked the manager then he said not it's not allowed steers sells pork and pork is not allowed in Macdonald because people are allergic to it. I then decided not to pay for the fries and drink and leave. My question is how did they know that the burger that I had, had pork in it? I specifically explained that I don't like steers chips I love the ones from. MACDONALD'S. The manager in a sarcastic way said "yeah and I also love Macdonald's chips I know that feeling" Kindly make it clear if this is not allowed or not. Thank you Kind regards