D. Marker, Model Theory:
Corollary 4.3.24. The number of non isomorphic homogeneous models of $T$ of size $\kappa$ is at most $2^{2^{\aleph_0}}$.
Proof.
Homogeneous models of cardinality $\kappa$ are determined by the set of types realized. Because $|S_n(T)| ≤ 2^{\aleph_0}$, the number of possible sets of types realized in a model is at most $2^{2^{\aleph_0}}$.
I can't understand why the sentence which I've made it bold in the proof is true. Would be grateful for your help.