10 minutes is the average.
Perhaps this web page will help you understand:
https://en.wikipedia.org/wiki/Average
Since the majority of blocks are faster than 10 minutes, the only way you can have an average of 10 minutes per block is if some of the blocks are significantly slower than 10 minutes. That's the way averages work.
If I want an average of 10, over a set of 10 items and I have:
- 8
- 2
- 6
- 2
- 3
- 1
If I have:
- 4
- 2
- 5
- 2
- 3
- 1
- 6
As you can see, the more values you have less than the target, the larger the few remaining numbers will be.
The time between blocks is actually completely random, and there is nothing enforcing any specific time for any specific block.
Think about rolling a six sided die.
On average over the long term, you will roll each digit about 1/6 of the time.
However, there is nothing enforcing that any specific roll will be any particular value. It is entirely possible to roll a 6 five times in a row.
Similarly, with bitcoin blocks, the long term average is 10 minutes per block, but it is entirely possible to have several blocks within a few seconds of each other, or some blocks that take as much as an hour. The longer the time between blocks the lower the probability that it will happen. Shorter times have a much higher probability and therefore are FAR more frequent.