yeah, i get that, but many people just use u because its more accessible (ascii and qwerty compatible), similar to writing μBittorrent as uBittorrent. imo i dont think its too big of a deal if it doesnt match the word micro, since μ is already a bit of a stretch. this is just my opinion, im not advocating for a SI reform or anything :)
it is a dynamically linked library, meaning its not in the compiled binary, but its assumed to already be on the system. as opposed to a statically linked binary. this lowers the file size of the binaries, because most will use the standard library.
edit: this may not be 100% correct, but its the general idea