Correct! Derec simply uses the word as a euphemism for black people, while disingenuously asserting that this isn't the case by pointing to the one time he didn't.
That describes about 1/3 of the population of the US.
2/3 if you ask Canadians.
A thug is defined as a violent person inferring criminal. How can this relate to 1/3 of the US population?
Words can't "infer" anything.
Taking the origin of the word see one of the definitions of infer below.
Dictionary.com
http://www.dictionary.com/browse/thug?s=t
Word Origin and History for thug Expand
n.
1810, "member of a gang of murderers and robbers in India who strangled their victims," from Marathi thag, thak "cheat, swindler," Hindi thag, perhaps from Sanskrit sthaga-s "cunning, fraudulent," possibly from sthagayati "(he) covers, conceals," from PIE root *(s)teg- "cover" (see stegosaurus ). Transferred sense of "ruffian, cutthroat" first recorded 1839. The more correct Indian name is phanseegur, and the activity was described in English as far back as c.1665. Rigorously prosecuted by the British from 1831, they were driven from existence, but the process extended over the rest of the 19c.
I am using this definition
http://www.dictionary.com/browse/infer
to hint; imply; suggest.