Originally Posted by
Stranger
This is the correct answer.
The OP's question is not really properly phrased. Issue is not whether customs are is airside or landside. Passengers coming from outsde the country are supposed to be rescreened. This is simply policy.
This is also why airports such as FRA have just recently instituted screening for international pax prior to transiting either to Schengen or another international flight. IE I had to be re-screened in FRA when transiting from PEK to YYZ.