What makes an English language book?
A publication with 15,000 English language words (words, words with meaning or sentences, with or without graphics) relevant to a specific topic written on at least on 50 pages comprises an English language book.

What makes an English booklet or pamphlet?
A booklet or pamphlet is 5 to 50 pages including cover pages, with fewer than 15,000 English language words (words, words with meaning or sentences with or without graphics).

Is the conclusion based on research or whimsical?
Research.

How did I reach to the conclusion?
Research.