[oksusu]

Hi,
 
So I was reading my book and read "1-octene on bromination with NBS yields a mixture of 3-bromo-1-octene (ca. 18%) and 1-bromo-2-octene (82%) - both cis and trans isomers"

I understand how the trans isomer forms for 1-bromo-2-octene.
My question is how does the cis isomer form for the 1-bromo-2-octene (82%) Is it simply because of bond rotation about the single bond during the resonance form?? Are there any alternative reason or am I totally wrong? Apparently there are 2 explanations to this question...
 
Thanks!