Yes, it's a real Windows feature called Delivery Optimization (enabled by default on most editions).
Your PC can download and upload Windows update/app files with other PCs on the internet (like a limited P2P network) to reduce Microsoft's server load. It uses some upload bandwidth, but not a fixed "40%"—that's hype. It rarely tanks gaming ping noticeably, but can on metered/slow connections.
The gpedit.msc fix you saw (Download Mode = 0) fully disables peer-to-peer sharing. Easier: Settings > Windows Update > Advanced options > Delivery Optimization > toggle off "Allow downloads from other PCs." Restart after.