Why is Luke considered an inspired book

When the author so assertively says in the introduction

Inasmuch as a number of writers have essayed to draw up a narrative of the established facts in our religion ² exactly as these have been handed down to us by the original eyewitnesses who were in the service of the Gospel Message, ³ and inasmuch as I have gone carefully over them all myself from the very beginning, I have decided, O Theophilus, to write them out in order for your excellency, ⁴ to let you know the solid truth of what you have been taught.

He is relaying what he has read or others have said. And nowhere does he claim inspiration from anywhere, not even from a joint.

Whose work is he referring to? Who had written these earlier gospels and why doesn’t he mention their names?

And if he has gone carefully through them, let’s for the sake of argument say it was Mathew he read, why does his genealogy of Jesus H. Christ differ from it?

There are 7 miracles only Luke knows where he got. Did he make them up? If he is a historian, does he treat of history when he writes of miracles? Should we take him seriously as a historian?