It's not about the difference between sidereal and tropical zodiacs (of course the only "right" is sidereal), but about the relation between zodiac signs and 360 degrees ecliptic.
So, if you look at Saturn in the night sky now you'll see that indeed it is in Libra constellation and not in Scorpio.
But it turns out that constellations and zodiac signs are two different stories and have different boundaries.
So, from the astrological point of view, Saturn is in Scorpio, meaning it is situated in a portion of ecliptic that has been assigned to this sign. The signs start from aries and each is 30 degrees long on ecliptic, although signs themeselves (constellations composed of stars) are not of equal length, hence my initial confusion.