ERA5 geopotential level 1000 negative values

When I download the pressure level 1000 of geopotential and convert it to netCDF I see that negative values appear in the minimum values, is this correct or this should be considered as an anomaly instead of absolute values?
For example, for monthly g1000 and the date 201812, the grib downloaded is g1000_201812-monthly.grb , and then converted to netCDF:
msamso@bsces108116:~/Downloads$ cdo -O -R -r -t ecmwf -f nc4c -z zip_4 -copy g1000_201812-monthly.grb
gribapiGetTsteptype: Time stepType avgua unsupported, set to instant!
Warning (gribapiDecode): Conversion of gaussian reduced grids unsupported!
cdo copy: Processed 1038240 values from 1 variable over 1 timestep [0.16s 90MB].
msamso@bsces108116:~/Downloads$ cdo info
-1 : Date Time Level Gridsize Miss : Minimum Mean Maximum : Parameter ID
1 : 2018-12-01 00:00:00 100000 1038240 0 : -1927.1 699.85 3272.6 : 129.128

Thank you very much in advance.
Best regards,

Negative geopotential heights are physically reasonable.

Consider a hurricane, for example, where the sea level pressure in the eye is something like 950hPa. The “1000 hPa” level doesn’t exist, but we can pretend it does by acting as if the atmosphere extended below the surface.

Thank you very much for your answer, now it is clear for me.
Kind regards,