That transaction has exactly 1 sat/vb fee rate not below it since it pays 5048 and has 5048 virtual size.
Yes, but it was created by joining transactions that were below 1 sat/vB fee rate, see sighashes.
Fees decreased because of the price not because "traffic" went somewhere else.
People don't want to go below 1000 sats/kvB on-chain, so if you want to make any transaction with lower fee rates, you can get it accepted only in separate networks, where transactions are batched in a trustless way, to form something that will appear as 1000 sats/kvB on-chain, but for users it is cheaper during making off-chain transactions.