There are many people that talk about long tails that have no clue what they are, they are just repeating what they have heard or read somewhere. It’s often a case of the blind leading the blind.
If you think the number of words in a keyword has anything to do with whether or not it is a Long Tail, then you clearly have no idea what a long tail keyword is and you need to forget whatever you have been taught because clearly your source is badly misinformed.
Simply put a long tail keyword is a low volume keyword, as compared to the main keywords within a data set. More specifically when there are substantially more low volume keywords than high volume keywords, the tail of a power-law graph appears as a long tail and the terms within that long tail of that power-law graph are considered the long-tail terms.
A keyword can be very short, even a single word, initialism, acronym, etc.and still be a long-tail keyword.