The image contains 165 bytes of assembler source text at $5900–$59A4, cut off at both ends. Decoding the high-bit characters reveals comments such as * CHAR 97 and graphics bytes written with DFB directives.

Each character is defined by two lines of four bytes. Some match tiles used in the finished game’s wizard sequence. Character 97 includes DFB $F0,$C0,$00,$00 followed by DFB $3F,$FC,$F0,$03.

The high-bit text, asterisk comments and $8D line endings fit Apple II-style assembler conventions. That identifies a format, not necessarily the computer used to develop the game. The exact assembler remains unknown.

Byte evidence: https://github.com/henols/c64_games/blob/main/bruce_lee/docs/development.md