A perplexed situation

The waitress appeared with our orders and we enjoyed the meal. I was having good time with Chloe and Duke but I wished Enzo was here, too. His work was obviously much more important than me, what am I wishing for? 

"That's non-vegetarian."

Duke nearly shouted making me come out of my thoughts as I saw Chloe was taking a slice of pizza kept in the center of the table. 

"Yeah, I ordered non-vegetarian pizzas. Is it not good?"

I asked seeing Chloe conflicting in her mind as she placed back the slice. 

"No, it's good but I was just warning her."

Duke said simply. 

"Warning?"

I didn't know, what they were talking about. 

"Yep I am a vegan and meat doesn't suit my body. I am allergic to non-vegetarian food."

She told me and I nodded, taking in the situation. But how come Duke know about it?