That is confusing two different issues. The thrust of the point being made is that the 'unnatural' argument won't work. The fact that there are similarities doesn't mean there are not valid differences.
The puritans and religious bigots will just have to fabricate other intolerant arguments instead, I suppose.

You forget that with most other animal species the young mature very fast.  You also forget, even though you quoted the line, that the article states, "engage in oral sex with each other."  It said nothing about sex with adults.  You also may not be aware that sexual experimentation is quite common among human prepubescents, though as a society we attempt to curb that behavior.  You didn't comment on this but you may also want to consider that in most other animal species their isn't a "weaker sex" so rape is usually not a consideration since the would-be rapist might just as likely get their ass whooped if their intended is not amenable.

That paragraph isn't suggesting children "help out in the bedroom" it simply states that the chimpanzee young try out oral on one another. Being that we are (supposedly) more sophisticated mammals, we do not participate in foreplay or fornicate in front of our children because they would be too curious. Just like anything, the young learn from their parents.