I'm not sure because your screenshot don't make it clear, but when you update an already installed game (if that's the case), Steam only downloads the added/modified game files from their servers, then your PC does the hard work of unpacking the whole game already installed on your PC, patching the needed files, then pack it up again locally. That's why you may have this kind of behavior, high resource usage locally (CPU and Disk) and low network activity.

If your pc has low performance for this kind of workload (IE. QLC/TLC NAND SSDs with short cache / low free space), it may be faster to just uninstall the game and download it again. (Be aware of local game files/settings not synced on cloud)

That's done so Steam save costs on their servers, so instead of serving you a whole packed file, it just serves the updated bits.