It isn't a dig. It's a logical follow up question.
In that case, allow me to apologize for taking it the wrong way.
You obviously think that ritual alone doesn't qualify. So what else is needed?
I think that a religious rationalization needs to be attached to the ritual, either before or after the first occurrence of the ritual, but I think I have already said that. In addition, there needs to be a sufficiently powerful and/or persuasive person to convince others that the ritual is a necessary component of that religious tradition. There are likely other factors at play, but I honestly have not put much thought into it, until you asked the question.
I think my hypothesis is elegant. That doesn't make it true. All I want to know is what you would add to the equation to make it complete. I thought comparing it to biology was fun and playful.
I don't necessarily disagree with your hypothesis, as long as you are leaving the word 'might' in there. My point is that there are numerous rituals that do not give rise to religion, so we can't say that just because a ritual is taking place that it is a 'proto-religion', though we could say that it MIGHT be a 'proto-religious' ritual. We simply don't know until well after the fact, when the religion is formed, and that ritual is a part of it. Also, to further separate the concepts of 'ritual' and 'proto-religion', things other than rituals can give rise to religion. An event, or an idea could be 'proto-religious' in nature, with no ritual involved until well after the formation of the religion.
So, to say that the ritualistic behavior of the chimps in this case IS 'proto-religious' would be unsupported, however, it would be just fine to say that the ritual MIGHT be 'proto-religious'. Until the chimps evolve to a state where they are able to communicate religious thought with us, tell us that they are worshiping the trees, and that the ritual of throwing stones at the trees is part of that religion, all we can do is offer speculation based on observations of how human religion may have formed from ritual.