Consider the circuit diagram shown. You can recognize the two resistors connected in parallel.
With the ohmmeter you measure a total resistance of 500 Ω. The formula describing this is a bit more complicated...
1/RTotal = 1/R1 + 1/R2
You can rewrite the formula to get...
Rtotal = ( R1 × R2 ) / ( R1 + R2 )
= ( 1000 Ω × 1000 Ω ) / ( 1000 Ω + 1000 Ω )
= 500 Ω
The total resistance of a parallel circuit of resistors is therefore smaller than any of the individual resistances.
The result becomes clear when you measure the currents...