Your suggested sentence is fine.
If you want, you can also
- thank the other person for spotting your mistake and
- explain why you were mistaken.
If you made the mistake, others might as well - after all, you mentioned that the repo is a tutorial, and tutorials are aimed at beginners. Maybe there's a way to improve the tutorial so that others won't make the same mistake you did?
Oops, my bad. Everything was correct after all!
I initially thought that foo needed to be initialized to avoid frobnicating the bar, but after reading your comment and re-reading the code I realized that baz was explicitly designed to handle uninitialized foos. Thanks for spotting my mistake.