Gas , refers to the amount of gas remaining after the execution of the STATICCALL function while gasCost is the cost of static call. The former is available for other calls in the transaction and refunded if not used .
The cost of STATICCALL is 700 gas.
To verify, at step 323 , you have a STATICCALL
But at the next step 324, ...
From the official documentation:
The first four bytes of the call data for a function call specifies the function to be called. It is the first (left, high-order in big-endian) four bytes of the Keccak-256 (SHA-3) hash of the signature of the function. The signature is defined as the canonical expression of the basic prototype without data location ...