Why is this happening. There must also be a difference of at least 10 minutes between the blocks.
If high fee is paid that can get bitcoin transaction confirmed in the next block, but bitcoin transaction confirmation are not instantly, it do take 10 minutes in average, the algorithm was just set in a way it should mine new block in approximately every 10 minutes and get transactions confirmed along, but that does not mean transactions is exactly 10 minutes. Even to be surprising, the next block can take 30 minutes at times, or might take less than 2 minutes at times. So, if you see a bitcoin transaction that is confirmed before 2 minutes, do not be surprised.
This is basically because you are offering a higher incentive for miners to include your transaction in the next block.
Maybe OP made a transaction that got confirmed before 10 minutes, and we know that next block at times can take less than 2 minutes. Maybe OP paid high fee, and his transaction was included in the next block, and take less than 2 minutes (or far less than 10 minutes before it was confirmed), which is very possible.