Everything is relative... to what is in the scene and what metering mode your camera is in!
when I meter an 18% grey card with my Canon, its reading matches the reading that I get with my Minolta incident light meter. If I follow that reading, an 18% grey 'mid tone' ends up just to the left of center on the histogram.
There have been threads on forums in the past, discussing the fact that you actually need to meter a 12-13% gray tone, in order for 18% 'mid tone' to truly be recorded in the center of the tonal range (middle of histogram).
You will also hear mention of needing to bump exposure a bit to the right, in order for ETTR practitioners to move highlights to the right edge of the histogram.
Exposed as metered +0.66EV