How do they know it's a rocky fragment (ie, micrometeorites) and not one of the zillions of pieces of orbital debris zipping around?
A particle doesn't need to be rocky to be a micrometeoroid. The term covers all bits of stuff in space in a certain size range (usually <1 g) , both natural and debris.
I think the question relates to the bit that says...
It is thought the damage was caused by the impact of a high-speed rocky fragment flying through space.
Someone, at some point (maybe in the news department, but maybe actually in Mission Control) has said that it
is (likely to be) rocky. Which makes it a micrometeoroid unless we've been sending rocks into orbit.
That made
me wonder if this was therefore a "bit of comet dust" or somesuch, which tends to arrive in bunches (incredibly spread-out bunches, to cover the whole sky as swept out by the Earth over a few nights, but still the chances of a second bit being near in time and space to a first bit is greater than one being in any other random time and space).
Obviously man-made/-sourced MMs are ubiquitous and ever (if individually fleetingly) present, but if the classification is not an uninformed editorial misclassification then we can presume the rockiness is an important distinction. (Maybe the calculated direction/power of impact was explained better by something not in any trivial orbit?)
But, at its heart, I just needed to pad out tje link