There is no discrepancy. The S2 L1C contains a Cloud Mask. It is located at GRANULE…\QI_DATA\MSK_CLOUDS_B00.gml. Table 18 (Granule / Tile PDI Quality Indicators) of the [PSD] refers. Additional information can be found at https://sentinel.esa.int/web/sentinel/technical-guides/sentinel-2-msi/level-1c/cloud-masks
S2 MPC Operations Manager
Yes, as Jan said it is available also in the ESA data.
It is just provided as vector data and needs to be converted to raster data by GEE.
This is also done when you open the official ESA data in SNAP.
There the cloud mask are available also on all three resolutions:
Beside the cloud masks also other masks are available.