We’ve posted other versions of this video before.
Possibly the greatest weakness of the T-72 series tanks is the storage of its main gun ammunition. The 2A46 125mm smoothbore tank gun uses an autoloader. It fires sabot rounds, High Explosive Anti-Tank (HEAT) and High Explosive Fragmentation (HEF) rounds. The ammunition is separate loading, with the autoloader first loading the projectile, then a separate propellant charge. The ammunition is held in a horizontal position on a carousel at the bottom of the turret basket.
The FGM-148 Javelin missile, using a fire and forget imaging infrared seeker, has a two stage tandem HEAT warhead. The first smaller warhead is to detonate any Explosive Reactive Armor, while the second warhead is intended to actually penetrate the main armor.
You’ll note that the Javelin flies a lofted trajectory when used in the anti-tank role. Among other benefits, this means it is attacking the top armor of the tank, virtually always the thinnest armor of any tank.
If I had to guess, I’d say the explosive jet from this particular shot actually struck either a HEAT or HEF warhead in the carousel. Virtually any HEAT warhead penetration will usually set off the combustible propellant cartridges in the carousel, causing complete destruction of the T-72, but that usually doesn’t result in the utter devastation seen here.
As a contrast, the M1 series of tanks, while it uses semi-combustible propellant charges for its main gun ammo, places that ammo in the rear of the turret bustle. There are blast resistant doors separating the storage from the inside of the turret. On top of the storage are blow-out panels designed to fail and vent any explosion up and away from the crew in the turret. The vehicle might be destroyed, but the crew would have a good chance of escaping with their lives.