This morning's Sudoku from the UK Guardian newspaper https://www.theguardian.com/lifeandstyle/2020/feb/08/sudoku-4704-expert was classified "expert". The puzzle has 28 given values.

My Excel based software is designed to post those elements of the solution that can be solved simply by applying the Sudoku's definition rules, leaving me to scratch my head over the more sophisticated stuff. To my surprise, the repeated application of the definition rules solved the whole puzzle. https://drive.google.com/open?id=10FfLrMrFcyzGkZkmKM2HiRsgMwmciljz

Was the difficulty classification wrong?