You are using scram to build some version of CMSSW?
In this forum you’ll find help for questions about ROOT itself, but I’ll try to answer: I guess the first dictionary is related to ROOT (since CMSSW provides ROOT). LCG stands for LHC Computing Grid, but don’t know what’s in that dictionary.
The name are essentially historical at this point. “root dict” indicates that the input/configuration of the dictionary generation step was done via a LinkDef file (using #pragma link ... syntax) while “LCG reflex dict” indicates that the input/configuration was done via a selection.xml file (in XML format).
There used to be a distinct product named “Reflex” that was part of one of the LCG software suite.