I sorta feel like you're making the mistake of inferring from the premise "they are biological machines" a conclusion which does not follow from the premise, which is that they are therefore necessarily so drastically different that they experience emotion differently from humans. I feel that is a non sequitor.
While, granted, you could interpret it that way, but that would add your own perception of how a biological machine would operate into the premise to form your conclusion. The interpretation of the Nomad way of acting, feeling and conveying this to humans has already been done years ago, however and I doubt it can be changed just like that.
However, this is only tangentially related to the initial question of the thread, which pertained to the expansion of the Nomads. The answer was provided by Antonio already, but the simple summary is that, while they would like to get rid of humanity because they are in the way of the Nomads colonizing Sirius, they do not have the power to do so.