Are the maximal noun phrases found by this code incorrect?

I was reading the accepted answer
to this question on natural language processing

In there an english sentence is given:

"Natural language processing (NLP) is a field of computer science, artificial intelligence, and computational linguistics concerned with the interactions between computers and human (natural) languages."

Now my grade school understanding of noun phrases suggests that the maximal noun phrases here are:

"Natural language processing (NLP)"

"field of computer science, artificial intelligence, and computational linguistics"

"interactions between computers and human (natural) languages"

But the maximal noun phrases that the code finds are:

"[‘natural language processing’, ‘nlp’, ‘computer science’, ‘artificial intelligence’, ‘computational linguistics’]"

Is my intuition correct and this computer code is NOT GIVING maximal phrases or do I have an incorrect understanding of noun phrases.