Hi hi! First of all, thank you for playing <3 Now, to answer the questions. No, the error isn't intentional, I wasn't aware it's happening. This is a result of a bit of code that would leave a "note.txt" file in your game files, which then could be found and read as a bit of an easter egg. This was the first ever project I made almost 3 years ago and it worked back then, so I assume something must've changed or get messed up along the way; fixing it isn't my priority now but I'll get to it once I have a slower day.
And when it comes to the ending, it does end on "It was me", so you're not missing anything, don't worry.
Anyway, once more, thank you for playing <3 Didn't think BitW will still receive some love after all this time