Essential Qi

In Chapter 3, section 2, 1.3, it says that nutrient Qi (Ying Qi) is derived from the essential Qi of food and drink. In part 1.2 it says that pectoral Qi (Zong Qi) is formed from the essential Qi of food and drink and clean Qi (Qing Qi). Does this mean that some essential Qi of food and drink goes into making Ying Qi, and some essential Qi of food and drink combines with Qing Qi and makes Zong Qi?

Essential Qi is only a way of saying in traditional Chinese medicine, in fact it is quite the equivalent to the term of "Essence". Thus it makes quite a sense in the context.
So, this essence of food and drink for sure could participate in the formation of the Ying Qi and Zong Qi.
The so-called clear Qi is the one from the atmosphere.