So here we see the hooks that hold the base in place, marked with red arrows.

Obviously it would only take a very small degree of turning to get the clips to release.

I am suspicious of this little finger pointed out in green. Due to the condition of my mug, I am unable to tell if this is a locking mechanism or just some sort of guide pin.

If it is a locking mechanism, then it has been deliberately designed so that the mug cannot be opened again once assembled. I sincerely hope that isn't the case, but I can't tell either way for sure.