Because he probably didn't set a BASE receiver up on a KNOWN POINT. Or didn't use a BASE at all and just 1 receiver as ROVER which tries to determine it's location AUTONOMOUSLY which results as sub meter accuracy instead of sub cm accuracy. Can still get a FIX, but not at cm level... so a FIX at SINGLE AUTONOMOUSLY at sub meter accuracy only. Or he didn't use a single ROVER receiver with a CORS NTRIP connection to get sub cm accuracy.
With an RTK fix, why is it over 2m off from the BM?
Because he probably didn't set a BASE receiver up on a KNOWN POINT. Or didn't use a BASE at all and just 1 receiver as ROVER which tries to determine it's location AUTONOMOUSLY which results as sub meter accuracy instead of sub cm accuracy. Can still get a FIX, but not at cm level... so a FIX at SINGLE AUTONOMOUSLY at sub meter accuracy only.
Or he didn't use a single ROVER receiver with a CORS NTRIP connection to get sub cm accuracy.