The promise was also given to the father (Abram) of the child:
(to Hagar): “I will so increase your descendants that they will be too numerous to count.” And God fulfilled this promise (Genesis 25:12–18).
(to Abraham): “I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore. Your descendants will take possession of the cities of their enemies, and through your offspring all nations on earth will be blessed, because you have obeyed me” (Genesis 22:17–18).
The difference is found in the second and the third part of the promise given to Abraham.
10 The angel of the LORD also said to her, “I will surely multiply your offspring so that they cannot be numbered for multitude.”