Only darnassian citizens were saved, and a minority of them, of course they would fill the streets of stormwind since storwind didnt have any housing for them.
The fact is, the majority of night elf population died at teldrassil, how much and how many they will never know, but it was officially classified as genocide, so unless chronicles say only a few didnt escape or some BS, Teldrassil was and will ever be the biggest evil Sylvanas did.