Since you were stumped by this, I decided to check it out on my old 2DS. Looked up the CRC32 for Top Gear (NTSC) on DAT-o-MATIC and used to find the game file. Extracted the file from the zip, threw it into NSUI beta 27, set the injection method to SNES9x for Old 3DS Forwarder and let it build a .cia file. After putting it on my old 2DS and opening FBI, I was able to install it (see attached image) and can confirm it runs.
Not sure what your problem is here. If your game files are extracted when you're building the .cia file and you've got the right CRC32 for the NSUI database (not sure if this is a hard requirement for the SNES9x forwarder), I honestly can't imagine what's going wrong.
Are the oter .cia files your friend is installing actual 3DS (or DSi) games, or are they other injected games, like NES or GBA games?