SNA files are "snapshots" made by No$GBA, other emulators call them "save states", they save the current state of the game and are no valid save files.
Your save file isn't proper as well. The proper size is 128KB. Yours seems to be compressed.
To get proper save files in No$GBA there is an option called GBA Cartridge Backup Media, set this to FLASH 128KB Sanyo. Then open No$GBA.ini with a text editor, find SAV/SNA File Format and set this to Raw it is probably set to Compressed or something like that.
Make a backup of your save file before doing any changes!