Speculation: To me, it looks like the air in the tank wasn't pre-chilled before the addition of LN2. When LN2 was added to the tank it flash chilled the air cau

Speculation: To me, it looks like the air in the tank wasn't pre-chilled before the addition of LN2. When LN2 was added to the tank it flash chilled the air causing a partial vacuum which crushed it like a beer can.