Till Kinstler wrote:
But additional checks for transiting passengers arriving from outside
Europe seem to be common on european Airports nowadays as well.

These explanations do not quite make sense for me, but who said that
the security procedures needed to be logical? Passengers connecting
from on LH flight to another LH flight could have gone from one A gate
to another A gate, and these paseengers would not have been subjected
to the additional secuirty check. Similarly for passengers going from
one of the C gates to another C gate. I was not really paying close
attention, but it is possible that there was no air side security check
for going from C to A.