I think that's different because it's a name.

Here, you have two different names that you're trying to use to order a food that doesn't exist, so it's a bit different than something with a shared etymology and history. It would be like walking into a pub (again) and asking for "tako and chips," where "tako" is Japanese for "octopus." There's no guarantee that the dish exists or that the person you're talking to even knows what "tako" is.

Mandarin and Cantonese are essentially completely different languages, so you're just mixing phrases that the other person probably doesn't know.

I would guess octopus is an imported word, so what you're describing has in a sense happened. The scenario reminds me of the (probably inaccurate) origin story for chicken tikka masala, where someone asked for some gravy to go with their dry chicken tikka.

So maybe I could try ordering a char sui tsa sui, then I can regale my grandkids with stories about how I invented the world famous dish :)

I suppose food is literally a melting pot, of cuisines and culture.

Ps, I think octopus would go better with French fries.