I’ve been raising 3 Malawi eyebiters for 2 years and I have 2 males and one female , one male was getting aggressive to the female so I moved him over to the other males side, and they are doing this stance. One male darkened his colors and the other didn’t.
Well it's not always about strength either sometimes to outcome of a stand off may be decided by one of the 2 being just more aggressive/intimidating then the other one. It's not always necessarily because one is just outright stronger then the other. With the pic that ya posted I would say this was more of a dominance display rather then breeding behavior but like Milingu mentioned it's not too uncommon for same sex pairs to form. I even had a male pair of tinfoil barbs at one point that tried breeding.