Disabling the tntExplodes gamerule does not prevent TNT from exploding.
How to reproduce
1. /gamerule tntExplodes false
2. /summon tnt
→ It explodes, killing you and destroying blocks
Turning off the TNT Explodes gamerule will remove any ignited TNT lit by a player as soon as it was created. But if you use a command to summon TNT ( /summon tnt ) it will be created and after the fuse runs out, will explode regardless of the gamerule. This creates a loophole that could be used for obvious malicious purposes.