It’s a Japanese game compatible with the Japanese Master System or Mark III, which uses a different sized cartridge than the overseas SMS. The Japanese Sega SG-1000 used this same size cartridge, and the Japanese SMS/MKIII were backwards compatible with them.
The Samsung Gam-Boy (South Korean version of the Master System) also used the Japanese-style cartridges.
In Japan, they used the “Gold Cartridge” branding for first-party releases and “Silver Cartridge” for third-party releases.