Otherwise what reason would they have to worship him if he was just a human being and just a baby lying in a manger?
If a man or a slave “worships” his king or his slave master respectively in some sense then we know that it is because they have been placed in a relation of subordination and lordship by the authority of God and the government under him. Even though they are the same in being they are not the same in terms of their authority. Human beings are invested with different degrees of authority in relation to each other.
The angels who worshipped Jesus were not even in the same world order. So it was impossible that a natural circumstance could cause them to have a relation of subordination towards him.
The only possible reason that is left to explain for their worship is that Jesus is Jehovah in the flesh, the only begotten Son of God:
Hebrews 1 v 6 And again, when he bringeth in the firstbegotten into the world, he saith, And let all the angels of God worship him.