The 8 Birthday Keys are only in the 8 Story Mines.
They are not in the Challenge Mines.
In these types of scenarios it is much more easier to consult, study & follow the maps instead of the videos.
Have you checked out the relevant Wiki pages, quests, maps, videos, guides, walkthroughs & hidden gifts
You can easily find the solutions to puzzles if you check out the walkthroughs & maps.....everything is clearly & concisely highlighted.... including hidden gifts.
The Wiki pages & this forum will become your best friends throughout your Diggys Adventure journey.
VIDEO - PC