Is there something wrong with my stool being a dark forest green?

Feces that is very brown, especially light brown, means you have too much fat in your diet. Whatever poop is healthy for you doesn't mean it is healthy for everyone else. The article you read about feces being strictly brown was written towards omnivorous people, who do consume animal products. Vegetarians and vegans sometimes have different feces because of their change in diet. Have you eaten any with bismuth? Like pepto bismol or even aspirin? These can darken your stool temporarily. If you are eating healthy, are not experiencing any pains within your stomach and bowel region, and your feces remains the same color it may simply be the way you are digesting your food. I wouldn't worry about it, and congrats on becoming a vegetarian!