This is actually true only in specific cases. If you will use resolution that won't create equal square blocks that can be summarized equally (how this works was explained by other people), you will actually get less crisp image than native resolution.

So if you have 1920x1080 monitor, but you will use resolution lower than 3840x2160, you will get less edges, but image may be less crisp than 1920x1080 because of "approximation". Since we lack informations to properly descale image, it uses algorithm to figure out best possible result. Which varies and with low resolution difference image is more noisy, which means it's less sharp in result. It is more visible on displays with lower resolution. 900p image on 720p display will be visibly less sharp than 1440p image on 1080p display.

It's most visible with text if you set higher resolution on whole game instead of using internal scaler that renders only 3D objects at higher res while 2D HUD stays at native resolution.