PAS182 is a defined standard for data modeling within Smart Cities - it describes the relationships between various concepts so that data from local authority X should hold to the same data model definitions as data from local authority Y.
As the BSI web page states:
"The smart city concept model (SCCM) provides a framework that can normalize and classify information from many sources so that data sets can be discovered and combined to gain a better picture of the needs and behaviours of a city’s citizens (residents and businesses)."
FIWARE is concerned with the interoperability of the transfer of context data. Specifically the current state of a system (i.e. the now) is held within a context broker and all elements surround a context broker must interact with it using a defined standard NGSI.
Therefore there is no conflict between the two - you can base your data models on the terminology defined in PAS182 and create your own entities by communicating with a context broker using NGSI.