Exactly. In a free market, people freely trade their work for pay.
Wherever slavery exists, it exists because the government permits (or enforces) it.
His whole statement doesn’t make any sense. Does he really believe that “democratic” governments aren’t compatible with war, corruption, etc.?
And the Gulag was just a happy holiday camp, of course. No markets. State planning for everything, including mass arrests of innocent people for mere pretexts, so that they had the privilege of building railroads and digging mines in Siberia, dying of exposure, exhaustion, depression, or shot by a trigger-happy guard.
By comparison, North American slavery was a sinecure.