The NHL is doing a 24 team playoffs so that likely is where the idea comes from.

The initial report on the NBA resuming with a group stage presented a 20-team scenario. There’d be four groups with five teams each – one from each tier of the current standings:

Tier 1: Bucks, Lakers, Raptors, Clippers
Tier 2: Celtics, Nuggets, Jazz, Heat
Tier 3: Thunder, Rockets, Pacers, 76ers
Tier 4: Mavericks, Grizzlies, Nets, Magic
Tier 5: Trail Blazers, Pelicans, Kings, Spurs

Teams would play each other team in its group, and the top two finishers in each group would advance to an eight-team tournament (effectively the second round of the playoffs, though without conference splits).

But that format could apparently include four more teams.
The simplest way to expand to 24 teams would be adding a sixth tier then forming four groups of six. That’d mean adding:

Tier 6: Suns, Wizards, Hornets, Bulls
https://nba.nbcsports.com/2020/05/28...lude-24-teams/