I've heard about that. It's actually from a Chinese translation, not the original game.
Why it isn't.
That's right, it says to go to address 0x106000. Problem is, that address is beyond the 1 MB size of all licensed releases.
Also, notice this source code is trying to read "zeldag.gb", obviously a ROM file. Why would the real game's source code need to read its own output?
About Tintin in Tibet... never played it, is the GBC version a straight port of the non-GBC version?
Does the game actually contain enough content to warrant a size increase from 256KB to 1MB? If not, that could explain junk data ending up in the ROM.
(I suspect maybe GBC PCBs had a 1MB minimum. Only reason I can think of why Pong - The Next Level is 1MB, even though the actual used data is just over 64KB (the rest is all zeros, or mabye FFs.) )