The nine are Surya the sun, Chandra the moon, Mangala for Mars, Budha for Mercury, Brihaspati or Guru for Jupiter, Shukra for Venus, Shani for Saturn, and then Rahu and Ketu. Seven of them are visible bodies. Rahu and Ketu are not bodies at all: they are the two points at which the path of the moon crosses the ecliptic, the nodes, and eclipses happen when a luminary is near one of them. Indian tradition personified those points as the head and the body of a figure severed while drinking the stolen nectar of immortality, who pursues and swallows the sun and the moon and cannot hold either of them.
The word usually translated as planet is graha, from the root grah, to seize or take hold. That is a much better description of the working idea than planet is. A graha takes hold of a life for a period through the dasha system, exercises its character while it holds, and then releases it, and the practical business of Indian astrology is largely a matter of which graha is holding a person and for how long. Sanskrit forms the words for the eclipse-seizure and for possession from the same root, which is not a coincidence.
Counting the two nodes among the nine is therefore consistent rather than odd. What matters is not whether a thing is a body but whether it takes hold.