There are actually multiple ways of looking at anarchy.
One - The absence of being governed whatsoever by any group, by choice or not.
Two - No enforced government.
In the case of two, you can still govern through voluntary social structure. Often times people forget there's more than one meaning to the word anarchy. For example, many political anarchists believe this (this is taken directly from Webster's):
a theory that regards the absence of all direct or coercive government as a political ideal and that proposes the cooperative and voluntary association of individuals and groups as the principal mode of organized society.
On the other hand, sometimes people will describe a situation of chaos, where force (thugs, bandits, and so forth) rules as anarchy. They can't entirely be reconciled, because a band of thugs enforcing their choices and their laws (I want your money and land because I'm strong) on another, that did not enter into this social relationship by voluntary association, would fit under a definition of government or being governed. Think mini-Stalins that roam around and rule through force. So a political anarchist would not use Somalia as a good example of political anarchy, due to the fact there is a lot of coercion.
I would argue one can voluntarily associate with a group or membership, say, bay12games forum, which is 'governed' by admins and moderators. This group could also come to conclusions by democratic decisions, as well, for example, to edit my posts and put pictures of divine unicorns in. But, at any time, an individual could opt out, and could never be forced or coerced into participating in bay12games (unlike a true democracy, where the democratic rule is the law all must obey, so we could force you to participate in bay12games).
What you've described could be anarchy or not. One, you've voluntarily associated yourself with a class. Anarchy does not entail every decision must be entirely agreed upon at all times, that would simply be absolute consensus. If your class were forcing these decisions on you, that is, you must come to the class or you will be harmed, punished or jailed, even if you never signed up for the class, then it would be by no means anarchist.
The method by which they made their conclusion (the one-objection rule) doesn't quite fit under the idea of anarchy. Suppose everyone on bay12games wants to outlaw drinking beer for its members. I could simply say, I don't agree to this rule. The rest will still agree to live by that rule and it will apply to them, just not me. But perhaps one of the founding rules to voluntarily associate with bay12games is to obey the rules that are decided upon. If your class were to exactly resemble political anarchy, people would have the choice to opt out of the decided grade system, but it gets confusing because you have the choice to opt out of the class. So my point...political anarchy is not such a clear cut concept. Basically, your classroom is not being anarchist in nature, but it could fit within a political anarchist system, if that makes sense.