If there were other alien life He could have separate arrangements for them now as necessary so you are right not to mention them but He did not have to He could explain to them there are other created things in heaven that later would be known at end.
And it could be that He chose not to explain it to them just as He chose not to explain it to us.
Consider the following possibility:
On the other side of the galaxy is an inhabited planet called "Snorflex" (Actually, its true name is unpronouncable, as Snorflexians have four mouths and eight tongues, but "Snorflex" will do).
Now, assuming that God loves
all His children, it stands to reason that He loves the Snorflexians as much as he loves us: no more, no less. So just as He sent His only begotten Son to us, He sent Him to the Snorflexians as well. And just as He came to us fully divine and fully human, He was there, fully divine, and fully Snorflexian.
So "Jesus Christ," under a Snorflexian name (which would give you a hernia if you tried to pronounce it) appeared and ministered to the Snorflexians as one of them, reconciling them with God the Father.
Why not? And while we're at it, since God is in no way bound by the limits of time or space, Jesus could have walked among the Snorflexians at the exact same time he was ministering in ancient Israel... After all, as miracles go, how hard is it to be in two places at once?
And why don't we know any of this? Because what happens with the Snorflexians has
no impact whatsoever on our salvation... and vice versa. Why burden us with unnecessary things?
Actually God is the same yesterday today and forever people may change but His word never changes His truth never changes and His character which is merciful to any living person. It is everyone who is responsible to repent and have a love for the truth.
And that applies to humans and Snorflexians alike, right?