That's probably because the stream was in regular x264 codec. If it was x266, it would've consumed significantly less data.
x265 provides same quality at 60-70% of the size of x264.
Whereas, x266 claims to provide same quality at Half the size of x265.
The H.266/VVC is the video coding standard the succeeds the H.265/HEVC standard, promising the same quality at half the size for 4K and 8K content. Read on!
www.xda-developers.com