He says it in repect of the Father just like the Father says it in respect of the Son. Here's one where the Father calls the Son Lord and God, do that mean the Father has a God? And the Father shares His glory with the Son in verse 6 & 13. Verse 12 goes with Hebrews 13:8.
Hebrews 1:5-13
"5 For to which of the angels did God ever say: “You are my Son, today I have begotten you”? Or again,“I will be to him a father, and he shall be to me a son”?
6 And again, when he brings the firstborn into the world, he says,“Let all God's angels worship him.”
7 Of the angels he says, “He makes his angels winds, and his ministers a flame of fire.”
8 But of the Son he says, “Your throne, O God, is forever and ever, the scepter of uprightness is the scepter of your kingdom.9 You have loved righteousness and hated wickedness; therefore God, your God, has anointed you with the oil of gladness beyond your companions.”
10 And, “You, Lord, laid the foundation of the earth in the beginning, and the heavens are the work of your hands;11 they will perish, but you remain; they will all wear out like a garment,12 like a robe you will roll them up, like a garment they will be changed. But you are the same, and your years will have no end.”
13 And to which of the angels has he ever said, “Sit at my right hand until I make your enemies a footstool for your feet”?
