you are not seeding by just leaving the window open on any peertube page. you are only seeding the specific video you have opened, if you have opened one, and probably not the complete video just the last segments you still have cached. this p2p sharing is mostly for when a certain video gets popular, to help with peek load, and for live streams. if the video was buffering for a long time it’s probably because the server did not have enough upload bandwidth, and no other viewer had the video segments.

there is another load balancing system that peertube supports, they can clone videos fromneach other and help serving them: https://docs.joinpeertube.org/admin/following-instances#platforms-redundancy