To do this, are they using some kind of modified payment terminal with extended range somehow? My understanding is that the NFC coils have to be very close, like single-digit cm to get any kind of power or data through.
At carnival in Bazil, you bump into people; Like, when they talk packed streets, they're talking body to body contact filling the street for blocks and blocks. All you'd have to do is put a terminal around your waist and you'd get close enough to activate NFC for hundreds of people just pushing through the crowd.
If I remember correctly, yes, they had a modified terminal that picked up cards more than a meter away. But the other comment is overestimating the damage, there is no way they took 'hundreds of thousands', more like thousands in total. Especially since contactless payments usually have a very low transaction limit (something around R$100 in Brazil).
(Reply depth reached) I guess if you're filtering through a big crowd then indeed you could get really close to people and their wallets. I thought GP was saying you could immediately skim every person in a crowd at once.
https://en.wikipedia.org/wiki/Brazilian_Carnival#/media/File...