This is the METAR at the approximate time of departure, I doubt that it is considered adverse (from meteocentre.com)
EDDF 25/1420 6.2 1002.0 3/1 87% 110 2 -RA FEW007 SCT011 BKN018 TEMPO BKN010=
Not a METAR format that I am used to, but it appears to be adverse weather at 3 deg in the rain it certainly calls and engine run up and delayed flap extention. Also the METAR says nothing about the ground conditions. However, the engines should have been runup and the flaps extended and checked prior to the roll. I would imagine passengers may believe they have started to takeoff during the runup.