He was wearing a bird head-dress, as his totem animal was the bird (see pole). But the aurochs was bigger and meaner and flattened the bird-hunter’s dick. 
Maybe it tells us more about social organization, than about art. The lurking question is “Why didn’t some smartass draw whatever he damn well pleased?” The answer would be that individuals had far less freedom to do so, than would be suggested by the modern Warhol paradigm.
Addaura Cave in Sicily has petroglyphs ranging from Upper Paleolithic in age to Mesolithic. It is famous for its early human figure representation alongside animals. The humans are not throwing spears, but holding a ritual. A group of naked people wearing bird masks and animal masks over their heads dancing in a circle, in the middle of which two nude male figures sporting erections lie side by side, twisting their bodies about together and apparently doing things to each other with their erections. Gay? You bet! 
Anyhow, I just wanted to note that while Addaura Cave has plenty of human figures, none of their faces are shown, only masks; either that or human heads with faces left blank.
Daniel Quinn proposed the idea that most cave paintings are instructional aids. During the off season, veteran hunters drew pictures on the walls of the cave for the benefit of the noobs, showing what the prey looked like, what their footprints looked like, and even suggesting points of vulnerability. Basically, they were like powerpoint presentations.
This would easily explain why they didn’t draw portraits. Training new hunters was way more important than mere art.
The best guess is that cave art was associated with shamanistic rituals, and that the animals depicted were depicted to summon the qualities the artists associated with those animals, either as totems of animals they identified with, or to help harness such qualities for themselves, or as part of important rites of passage ceremonies, such as initiation into adulthood.
Though of course there is no certainty about this, it is an explaination that fits what is know about shamanism in modern-day hunter-gatherers, the fact that the paintings were made in places humans would generally not otherwise go (deep inside lightless caves), and the intense conservatism of the images (some caves have paintings made thousands of years apart - which are nonetheless quite similar).
I’m reminded of the National Lampoon article on 30th Century archeologists. The picture shows a toilet with the comment -“we find one or more of these in every house, so we assume they have some religious significance…”
Or better …