Monitors are generally specified as 720p if they are close to that resolution. The difference between 1366x768 and 1280x720 is somewhat minimal, so for marketing purposes, most consumers will recognize something that says "720p" more than they will something that says "768p". The monitor most likely has a native resolution of 1366x768, and is just advertised as 720p. It can display anything at that resolution or lower, including 720p.
Here is a tip. If you want better performance (~5 fps) without completely ruining graphical looks, play stuff on 1280x720 on the 1366x768 screen. You won't notice a huge difference except in text.