When a new block is found, mining pools send miners a block template with no transactions so they can start searching for the next block as soon as possible. They send a block template full of transactions right afterward, but a full block template is a bigger data transfer and takes slightly longer to reach miners.
In this intervening time, which is usually no more than 1-2 seconds, miners sometimes get lucky and find a new block, using the empty block template.
This one was minute later
I take that back, it was a second later so yeah 👍
One thing worth noting is that the accuracy of block timestamps is not great. At the protocol level you only have a strong guarantee that a block's timestamp is within a couple hours of the real time. On the other hand, due to how mining pools and block templates work, trying to perform analysis on time scales below 10 seconds is likely a fruitless endeavor because block templates may be updated less often than that.
