I agree that it's probably people naturally favoring the "nicer" submissive chicken, who already is at a lower social standing with its pen-mates.
Although, in my flock o' four, the boss hen (BA) is the smallest and nicest, whereas the next friendliest (sex-link) is just kind of there as far as the other chickens go. The flightiest (EE) gets along well, too, tho' I rarely get to pet her.
The crankiest towards the others is the huge SLW, who is moderately friendly to me. She tends to pick on the EE, but gets her comeuppance from the other two if she tries something with them.
The EE for the most part is somewhat a loner, playing by herself and chasing leaves and other things that move while the others are busily scratching around--kinda ADD.
But she's the first to follow the BA (even with a trimmed wing) over the fence into the goodies under the holly trees--but when BA comes back, EE can't figure out how to come back over the fence herself. The sex-link sometimes goes over the fence, too, but only if one of the others goes first.
The SLW rarely goes over the fence--I think she's gotten too big and heavy. I'm sure the other three are glad to get away from her.