These cats are very unified in friendship. Are they head butting? I don’t think they are actually. These cats, looking so charming, are sleeping together, touching each other. Cats form friendships or become ‘associates’ when living in groups. Cats that are friends, like us, tend to sit next to each, to rub against each other and sleep next to each other. We as humans know all about that. Cats are no different.
Perhaps that will dispel the idea that some people have that cats are solitary, aloof animals. The are not. Particularly the domestic cat who has learned new ways over the 9 thousand years of domestication. Wild cats are a bit different. Also when there is a lot of space (large home ranges possible) feral cats will tend to be more solitary. Group living is an adaptation usually built on food availability.