Is " Rewarding nonetheless." A independent sentence?

Question

I'm doing a proofreading course and I came across this sentence in one of my activities. " The famous cognitive scientist on what constitutes an elegant written style, and why good style matters. Pinker is an academic, so this isn't light reading. Rewarding nonetheless." I want to know if this grammatical correct?

Answer 1

It makes sense in context, but is technically incomplete (as is the first sentence, which is nonsensical without the belated support of the second).

Answer 2

There are two incomplete sentences here. "The famous cognitive scientist on what constitutes an elegant written style, and why good style matters" doesn't include a verb for its subject, "the famous cognitive scientist." Similarly, "Rewarding nonetheless" is not a sentence, as it features neither a subject nor a verb.

Occasionally, incomplete sentences may be used in prose for effect, but this doesn't appear to be one of those times, as the paragraph isn't coherent as it is.