A note to this event >>/51365/
Orbán visited Brazil on the occasion of Bolsonaro's inauguration on 2019. Jan 1st. I don't think he does that for any head of state or prime minister.
But. I suspect one additional reason was the informal meeting with Zelensky which was pre-arranged. Hungarian media outlets mentioned visits of various diplomats, and talks about visits and whatnot to Ukraine. Our president, Novák Katalin also visited Ukraine back in August. I think these led up to this meeting in Buenos Aires. Orbán and Zelensky put themselves in a place where they can't just waltz into each other's country like nothing happened.