This is accurate. People built for strength look very, very different than people who build for definition.
Night Elf women come from a culture where the physical prowess of the females as fighters (the sentinels) has been valued higher than that of the males in their culture (who were primarily druids). They're going to have trained and built towards those values, especially because any changes to those values (around the beginning of World of Wracraft- about 12ish years ago in the lore timeline) are way younger than the vast majority of living elves.
I would agree that other races beat them in terms of potential strength, but on average, I'd say it's reasonable to assume that the average female Night Elf is stronger than the average female of other races.
((PS. The person above who mentioned the female dwarves: they actually do have the body type most accurately associated with strength training, compared to all other WoW races.))