Are constellations the same as celestial systems? If not, what's the difference?

It's different. Celestial system is the relationship between celestial bodies caused by physical gravity and other factors, such as the earth and its natural satellite moon, which constitute the earth-moon system. In addition, the solar system and the Milky Way are also celestial systems.

Constellations are generally divided by human beings observing the distance between clusters with naked eyes and imagining their ears. The stars in a constellation may actually be quite far away, or they may have nothing to do with celestial bodies at all.