Scripture refers to the saved as "sheep". Jesus explicitly referred to Judas as a sheep (Mt. 10:16 and Mk. 14:27). Furthermore, you cannot fall away from that which you never belonged. (Acts 1:25)
Remember Judas was destined to reign and rule with Christ as well...
"So Jesus said to them, 'Assuredly I say to you, that in the regeneration, when the Son of Man sits on the throne of His glory, you who have followed Me will also sit on twelve thrones, judging the twelve tribes of Israel.'"
Matthew 19:28
Sometimes sheep wander away and become lost. Jesus even gave a whole parable about sheep getting lost.
Luke 15:4-7. Something must belong to someone first in order for it to become lost.
You can’t lose something that isn’t your to begin wth.
Ergo, when Jesus said Judas was lost (John 17:12), he makes it clear Judas was at one time one of his "sheep” and thus one of his own.