Jayson Tatum wasted no time getting into the gym once the Celtics were eliminated from the NBA playoffs by the Cleveland Cavaliers.
He apparently has made significant strength gains and adding muscle will follow, though more slowly. The link between the two processes is poorly understood, and the confusion can be seen in Chris Mannix' tweets below. It is not unusual. Looks can be deceiving.
Some have made comparisons between Jayson and Kevin Durant. Durant came into the League at 212 pounds and now plays at roughly 242 pounds at 6'11".