Why is the term ‘Slave Dynasty’ regarded as misnomer?

Q. Why is the term ‘Slave Dynasty’ regarded as misnomer?

Consider the following statements :

1. Except for Qutub-ud-din Aibak no other ruler was a slave.

2. Only three rulers of this dynasty were slaves and even they were manumitted by their masters.

3. Technically only Qutub-ud-din Aibak and his immediate descendants were slave.

4. All the rulers of this dynasty did not belong to one family.

Which of the above is/are correct?

(a) 1 and 3

(b) 2 and 3

(c) 2 only

(d) 4 only

Ans: (c) 2 only