Tap water - black particles

I imessaged a photo to my contractor, his response was... How can it be, so strange!
When the plumber came, he explained that when piping was changed, there will be such particles left caught in the water heater. The way to rid of it is by flushing it all out first. That wasn't done. So theses particles got caught in the filter at tap and flow out in small qty.
Another lesson learned!