The manual of the original piece, the WH65 outdoor array (Y-shape) says:
Rain volume display range 0 – 6000 mm
Rain volume accuracy ± 10%
Rain volume resolution 0.3 mm (for volume < 1,000 mm)
1 mm (for volume ≥ 1,000 mm), or
0.01 in (for volume < 100 in)
1 mm (for volume ≥ 100 in)
the content of the tipping spoon of the WH65 rain gauge corresponds to 0.254 mm rainfall
the post you are referring to is not with a WH65 but with a WH40 rain gauge whose spoon content corresponds to 0.1 mm rainfall.
The highest rain rate I measured with my WH65 rain gauge was 102.7 mm/h
If you want to know the actual maximum, you will have to do tests yourself - and consider the to have a reference array
