Not to mention that Avgins had remarkable features which would be recognisable.
In fact, Aventurine's 'master' also noticed that he's from Sigonia.
The intel about Sigonian people and Avgins are also wrote by the Intelligentsia Guild which Ratio is from.

This man is a genius, there's literally no way for him to not have noticed it in their previous meetings, but their convo here suggested otherwise, and hence why it's implied that they were acting here.

Tho on top of all this long explanations, Ratio here literally said 'keep telling him' which easily implies that they work together regularly.
And ofc his lines about Aventurine imply this as well.

Now let's talk about these lines and the overall message that they were trying to convey to Sunday; 𝘁𝗵𝗮𝘁 𝘁𝗵𝗲𝘆 𝗱𝗼𝗻'𝘁 𝗹𝗶𝗸𝗲 𝗲𝗮𝗰𝗵𝗼𝘁𝗵𝗲𝗿.

Tbh, when there's discussion about them 'hating' eachother people always mean that it's Ratio who dosen't like Aven.
No one really argues about Aven not liking Ratio and hence, i also talk about Ratio's opinion about Aven more here.

So there's always this discussion about Ratio looking down at Aven and his past and overall, not liking Aven which makes 𝗮𝗯𝘀𝗼𝗹𝘂𝘁𝗲𝗹𝘆 𝗻𝗼 𝘀𝗲𝗻𝘀𝗲 at all.

To be able to understand Ratio's personality and character, you'll need to read his stories and do his quest (at the very least), hence why i'm gonna talk about those here as well.

First, let's look at the things that suggest Ratio dosen't like Aven;
His tone was mocking, he was agitated to work with Aven, him implying that no one is truely close with Aven, bringing Aven's past and implying that he's nothing to the IPC, and just overall being quite harsh.

Okay now let's debunke them.
It was pretty obvious that Ratio 'didn't' like working with Aven in the quest which Sunday even mentioned it, but now let's look at the program with Owlbert.

Here Ratio literally admitted that he dosen't think working with Aventurine is 'awful' and he even thinks he's a much better person to work with rathen than other fools. This is all despite the fact that Aven didn't even go to school.

Owlbert even 𝘀𝗽𝗶𝘁 𝗶𝘁 𝗼𝘂𝘁 that 'not awful' means 'outstanding' for Ratio.
(this was for some of yall who were gonna say 'well he said not 𝘢𝘸𝘧𝘶𝘭 which means he still thinks it's bad')