This would be helpful if the exact filtration used was cited. To the best of my knowledge after years of research, no municipal system filters below 1 micron, at least in the US. The cost to do so at that volume would be astronomical.
Our local plant doesn't even routinely test for NTM.
Dr Joe Falkinaham, the US expert in NTM in water has documented extensively the use of .2 micron filters.
https://www.atsjournals.org/doi/full/10.1513/AnnalsATS.201301-013FR