These Christians in Acts 11:20 didn’t categorize people as churched or unchurched, meaning they didn’t treat mankind’s main problem as poor church attendance.  Instead, it’s obvious that they classified everyone as either being reconciled to God through faith in Christ’s finished work or condemned by God because of their sin.  That’s why they brought the good news indiscriminately to all types of people and as a result of the Lord’s hand blessing their faithful efforts, those who repented and believed were added to the church.  Even then, their addition to the church wasn’t treated as the end goal, but those who professed Christ were instructed to persevere in faithfulness to Christ, which cannot be expressed merely by consistent church attendance.  Reason being, Christians still have the sinful nature to battle, the world to keep separate from and the enemy to resist.  That’s why it takes a lifelong fight of faith.