Saw an interview with the Bradly commander. He said they had a problem feeding AP and had to start using HE. IIRC the Bushmaster has a dual feed that allows selecting between AP/HE. I gathered that they had started with AP and then kept hitting them with HE just to keep ringing their bell.Part luck, part tactical skill, part the fact that it looks like they have the uranium depleted sabot rounds now.
The commentary also said that they'd knocked out the T-90's rangefinder early, and also the secondary explosions were the T-90's smoke grenade system being hit.