Didn't some escape the world and then turn back?

The short answer Settled

Yes: false teachers who were never saved. They heard the gospel, understood it, and cleaned up how they lived for a while. But they never believed, and they were never born again.

The same people

The chapter is about "false teachers among you" (2 Peter 2:1), "for whom is reserved the blackness of darkness forever" (2 Peter 2:17). Peter calls them "slaves of corruption" (2 Peter 2:19), and the next verse, about those who turned back, begins with for and is still about them.

A washed pig is still a pig

Peter speaks of two different escapes.

Believers are "partakers of the divine nature, having escaped the corruption that is in the world through lust" (2 Peter 1:4). God has given them a new nature, so the corruption no longer owns them. That is what it is to be born again.

Peter never says these men escaped the corruption. He says they escaped "the pollutions of the world" (2 Peter 2:20): the outward filth, the sins other people can see. They stopped doing those things for a while. But inside nothing had changed: "they themselves are slaves of corruption" (2 Peter 2:19).

His proverb shows the difference: "A dog returns to his own vomit," and, "a sow, having washed, to her wallowing in the mire" (2 Peter 2:22). A washed pig is clean on the outside, but it is still a pig, so it goes back to the mud.

The usual objection

These people "escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ" and then turned back, and "the latter end is worse for them than the beginning" (2 Peter 2:20). On this view they were saved and lost it.

Their end is worse because they knew the way and turned from it: "it would have been better for them not to have known the way of righteousness" (2 Peter 2:21). Knowing the way is not the same as believing it.

Many people hear the gospel and understand it, yet do not believe. Jesus had followers like this. He told a crowd of His disciples, "there are some of you who do not believe" (John 6:64), and then "many of His disciples went back and walked with Him no more" (John 6:66). They had followed Him and heard Him teach, and they turned back. Judas went further. He was one of the twelve, yet Jesus said, "one of you is a devil" (John 6:70). He heard everything the others heard and never believed.

The men in 2 Peter 2 are the same. They knew the way, but they never believed and were never born again. Turning back did not take away a salvation they had.

Going back does not by itself show that a person was never saved. Believers can live like unbelievers too. Paul calls the Corinthians "babes in Christ" (1 Corinthians 3:1), yet says they are "behaving like mere men" (1 Corinthians 3:3). The false teachers in 2 Peter 2 are different, and Peter has already said what they are: men who deny the Lord who bought them (2 Peter 2:1), "slaves of corruption" (2 Peter 2:19), kept for "the blackness of darkness forever" (2 Peter 2:17). What they knew makes their judgment worse.

The words behind it