@Pinotio.com is probably referencing the whole MEV (miner extractable value) discussion happening on Ethereum, in our case VEV 
. The gist of it is that the block proposers in a network can extract value by controlling the way in which transactions are ordered in a block.
The basic example usually involves DEXs, a miner can detect a significant trade transaction and can sandwich that between a buy and a sell that causes the detected trade to happen on the far end of the slippage spectrum while the miner extracts the arbitrage profits. Another more Celo specific example would be front-run arbitragers when cUSD is depegged.
Recommended reading:
- Maximal Extractable Value (MEV) | Chainlink
- MEV Explore - a projects that’s trying to democratise MEV in an interesting way.