I don't seed.
I live in a country with tight laws and actual cases of people getting sued over torrenting and seeding. With different financial outcomes between those two.
We are on the poor side and while I have some technical knowledge I'm not confident enough I can protect myself from financial trouble. So I unfortunately torrent through a VPN and have my client set to seed 0%.
It's definitely not. Copyright trolls send letters to all peers in a torrent swarm regardless of uploading/downloading. And in any case the bittorrent protocol uploads and downloads simultaneously - Even if the commenter is attempting to seed 0% they are still participating in the torrent swarm and uploading pieces of data to others in the swarm during their own download.
I have to assume that commenter's VPN is working as intended or maybe they have been lucky.