Mea culpa.
So summary:
If you have not changed the existing terrain on your property and the height difference on your land is minimal, there are, as already mentioned, only two remaining options:
1. The terrain on his property would be steeper. However, that does not explain the height difference of 30 to 50 cm at the boundary.
2. He has applied some fill to make his entire property level.
I consider option two more likely upon reviewing your pictures again.
Now it is necessary to prove that he leveled his terrain by adding fill. This would then obligate him under § 17 SächsNRG to organize/pay for the support.