According to a text string at 0xD274 in the later prototype (using the encoding A=0x0B, B=0x0C, etc.), this was developed by Software Creations.Edited to add:
Yep, the video clip with the ending screen that Hidden Palace tweeted
shows that that string is definitely used. As far as I can see, there aren't any individual credits hidden in the ROM, only the company credit from that screen.