The president of Argentina forgot to unschedule his victory tweet

I think it was published on purpose. After the match, a lot of people went to the street. I'd describe the feeling as sad but supportive. There was a strong rumor that Monday would be a national holiday. The x/tweet says that it will be delayed for another day.

I can't find a good source with hard numbers, but here are some photos: https://www.ambito.com/deportes/pese-la-derrota-miles-hincha... I read estimations from 7000 to 300000. The number 300000 is clearly false, because it's the number of people after the previous match that was defectively bigger. 7000 is to small, probably counting a small part just after the match.

The photo is near google.com/maps?q=obelisco+buenos+aires&gs_lcrp=EgZjaHJvbWUyBggAEEUYOdIBCDQ5MzZqMGo3qAIAsAIA&um=1&ie=UTF-8&ved=1t:200715&ictx=111 So it's like a 100m x 100m full of people. Not very overcrowed, so I guess like 2/m^2. But usually it extends like 3 blocks to the South and 3 t the North (100x600) and like 4 to the East and 2 to the West, but the street in not so wide (50x600). The density is not constant, so add 1/m^2 persons or perhaps .5/m^2. This rough approximation gives like 100000 persons.

You must also include side streets, and substract trees. It's more complicated. [After the previous gane, we went there but only like 3 blocks away to avoid overcrowded areas, and went to eat pizza nearby, like 5 blocks away.] Also there were smaller concentration in other parts of the city and in other cities.

Back to your question...

With a few thousands of people in the streets, there was a strong rumor that Monday would be a national holiday, when the players would arrive. I'm not sure why, but the decision in the x/tweet was to wait until the players organize some reception. Later Messi decided to wait another day in USA and the reception lost strength.

In my opinion, most people want to say thank you, but nobody was happy enough to organize a big party.