Zero_Stage=1 results in higher TFLOPS?

### Description

I am learning the chronicles_prequel, and I find the last table in the chapter indicates the higher TFLOPS is achieved with Zero_Stage = 1.
[Trying with ZeRO_STAGE=0/1](https://github.com/bigscience-workshop/bigscience/blob/master/train/tr11-176B-ml/chronicles-prequel.md#48-node-contenders)
Zero_stage=1 could reduce the memory cost, but how come it increases the performance with other parameter being the same?

Nodes | Size | ZS | DP | TP | PP | MBS | GBS | Mem | Sec/it | TFLOPs | Notes
-- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | --
48 | 181B | 1 | 4 | 8 | 12 | 2 | 2048 | 37GB | 120.29 | 134.02 | 02-21
48 | 181B | 0 | 4 | 8 | 12 | 2 | 2048 | 72GB | 137.34 | 113.02 | 02-21