This is because, we, the children of Adam u, carry a part of him genetically. Allah U addressed Adam u with all his parts because He is Allah. When He had given Adam u the covenant, the testimonies from his offspring were concealed in him, and every reproduction among mankind gets a part of Adam u. So, when Allah Usays:

﴾وَلَقَدْ خَلَقْنَاكُمْ﴿ “And We have certainly created you”, it means that He created you from the spine of Adam u. There is an indication here of the D.N.A and the genes.

﴾وَإِذْ قُلْنَا لِلْمَلائِكَةِ اسْجُدُوا لآدَمَ﴿ “And [mention] when We said to the angels, ‘Prostrate before Adam”: How could they prostrate to Adam, when prostration should only be to Allah U?

In answer, we say: “Who is the one who gives the command here?”

Prostration due to a command is actually prostration to the One who issues the command. The prostration here is a prostration of welcome and aggrandizement. It might also possibly not be in the form of the prostration that we know of.

He says: ﴾فَسَجَدُوا﴿ “so they prostrated” and did not say “They prostrated to him.” It is clear here that they prostrated due to the command of the One who issued the command, Allah U and not to Adam.