A player is assigned a connection number, the playeruid, visible via the command /ShowPlayers:
name, playeruid, steamid
VeryGames, 2890613232, 76561197970000000
This playeruid corresponds to the decimal value of the first 8 digits of the save file names, which are actually hexadecimal values.
If you're having trouble understanding, no problem.
By using this tool here and copying the name of the .sav file, for example 4BD87C2145BCD3916C05D8B0498854D8.sav, it will directly provide you with the corresponding playeruid.
In this example, the file is AC4B41F0000000000000000000000000.sav and the playeruid is 2890613232, as indicated in the result of the /ShowPlayers command.