[Glossary: Rollup] Sentence about transaction odering not totally clear

[smuu]

https://celestia.org/glossary/rollup/

Here it says: "It's layer 1s job to order those transactions and check that they are available, at minimum.".
As I understood, a rollup can post blocks to the L1, and the L1 orders the blocks. From the sentence, celestia can reorder the transaction inside the block.
Also, as I understood, there are transactions and blocks on the rollup and celestia levels. Blocks on the rollup level are transactions on the celestia level. So, maybe, point that out here.