Obviously the thief demonstrates faith in Jesus.
"Then one of the criminals who were hanged blasphemed Him, saying, "If You are the Christ, save Yourself and us." But the other, answering, rebuked him, saying, "Do you not even fear God, seeing you are under the same condemnation? And we indeed justly, for we receive the due reward of our deeds; but this Man has done nothing wrong." Then he said to Jesus, "Lord, remember me when You come into Your kingdom."" (Luke 23:39-42).
As the article you referenced points out, Jesus declares faith to be a work. "Then they said to Him, 'What shall we do, that we may work the works of God?' Jesus answered and said to them, 'This is the work of God, that you believe in Him whom He sent'" (John 6:27-28). Faith is something a person must choose to do. It is not a work of man because it is commanded of men by God. "But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him" (Hebrews 11:6). Therefore, the thief's faith was a work. He believed God exists and that Jesus would reward his followers.
We can also argue that confession is a work because it requires men to do something. "Therefore whoever confesses Me before men, him I will also confess before My Father who is in heaven" (Matthew 10:32). Confession cannot take place without a man choosing to do something that God requires. "For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them" (Ephesians 2:10). Repeatedly confession is emphasized as being done verbally. "If you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation" (Romans 10:9-10). And this verbal effort -- work if you will permit -- is connected to salvation. Therefore, the thief's confession was a work. He confessed that Jesus was innocent, that he was Lord, and that he would live again after his death. "Glory, honor, and peace to everyone who works what is good, to the Jew first and also to the Greek. For there is no partiality with God" (Romans 2:10-11).
In reference to his teaching, Paul stated, "For we are God's fellow workers; you are God's field, you are God's building" (I Corinthians 3:9). To the Corinthians, whom he taught, Paul said, "Am I not an apostle? Am I not free? Have I not seen Jesus Christ our Lord? Are you not my work in the Lord?" (I Corinthians 9:1). Therefore, by instructing his fellow thief on the cross, the thief was also working for God. Though he might not have touched the other man's heart, his words have touched the hearts of countless others who read the record of them. "Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your labor is not in vain in the Lord" (I Corinthians 15:58).
However you look at the thief, you see a man who did something with the last minutes of his life and accomplished work for the Lord. For this, he was rewarded. "And Jesus said to him, 'Assuredly, I say to you, today you will be with Me in Paradise.'" (Luke 23:43). Even though we don't have an opportunity to die on a cross with our Savior and take a stand with him, we can do the works God requires of us and be saved.