Two people having dinner together. Romance or friends.

I wouldn't think or assume anything?

If they are gazing adoringly into each other's eyes, then yes I would assume something.

But if they are just sitting, could be anything. People seemingly very close to each other are probably just best friends, or gay friends, people looking distant could be very long term couple completely at ease in silence.

I don't look at people for long enough to make up a story

I remember having a pub lunch with my father once (over 40 years ago). I’d have been about 20, and he would have been in his late 50s.

It was very obvious that the server didn’t know what to make of us (were we father and daughter or were we a couple) as he sometimes called me Madam and sometimes Miss and generally looked embarrassed. He clearly didn’t want to offend us by getting it wrong! I put him out of his misery after a while by loudly saying the word “Dad” when he next appeared.

I probably wouldn't think about it at all either.
The same thing happened to me, I was going for a meal with a friend after we had attended a talk, and couldn't understand why I couldn't get a table anywhere when I tried to book it the day before, when we got there the same thing, candles and flowers and a Valentines menu! (I am actually married so you would have thought I would have known it was V day but I am rubbish with dates - I did know by the time we got there but not when I was booking and it didn't really click that there would be all the V day stuff out!).

It wouldn't cross my mind to wonder tbh. I find it a bit odd that you'd give too much thought to the relationship status of two random people having a drink or a meal.

Tbh I always sit next to my husband so I’m normally more inclined to assume they’re friends but I know next to is not the norm. I also love a good people watch though so we normally make up silly stories about who they are.

I used to work in a pub though and you could always tell who was there with their wife/gf and who was there with their mistress. Every time.

Depends on what they’re wearing, how they converse and react to each other, tine if day etc.

Must admit, I do like people watching. My Dh and walked past a two people yesterday, and we both thought the ages were wrong for father and daughter, but to big a gap for a couple or siblings. For some reason, we both noticed these two people, and were both intrigued by them.

I wouldn't really pay attention and not care really.

But this does remind of the time a friend and I went for afternoon tea for my birthday as a fancy stately home/spa type place. My birthday is in February.

You have guessed it, it was decked out with roses and hearts for Valentine's day. It was all couples except for me and my friend. It amused me to think that everyone would think we were a gay couple having a romantic meal out 🤣😂

Or siblings

I’d think friends, couple or business meeting.

I think body language makes it perfectly clear. Obviously it's none of my business, but you can usually tell at a glance.

I prefer to sit alongside (at 90⁰ angle) rather than opposite someone when we're chatting anyway. It's friendlier and easier to hear what they're saying.