Yup your cat or possibly a coil pack on its way out. I have had this happen 1 time before and since it was over 2month ago and I'm still running on 4 cylinders it was not a coil pack. It must have been my cat blowing off/ releasing at that time I was reversing up a curb and I think it might have over fuelled.
Does it still seem to be running right ? if so I wouldn't worry to much just keep an eye on it m8 as it could be a coil pack. I haven't had it happen again but keeping an eye on it. Use the search and there is 100s of threads in reference to the eggy smell