A grist spreadsheet is an sqlite database:

$ file 2V3g4e7Xc6SYNPokEP8W5Q.grist

2V3g4e7Xc6SYNPokEP8W5Q.grist: SQLite 3.x database, user version 8, last written using SQLite version 3040000, file counter 6089, database pages 1059, 1st free page 927, free pages 139, cookie 0x355, schema 4, UTF-8, version-valid-for 6089