Well that's twisting his word, People do not turn to ashes in Hell but if believing that makes you feel better, alright.
Let's apply his
(bad) hermeneutic of eternality consistently in Scripture: God is thus not eternal either but will come to an end.
(of course I do not believe any of that; God is eternal, has always existed and will always be; i.e. "I am" Exodus 33&c)
To be honest, I think many come to false conclusions on eternality
(some Christadelphians on here for example) because we live in time, and in what we call the eternal realm there is no time which is difficult to comprehend if not impossible here in this state.
The limited language to explain, comprehend and express, i.e. finiteness here in this world complicates our understanding of things eternal due to that limitation in understanding.
We can only understand things according to time, we cannot comprehend eternal albeit the Spirit does help our understanding;
1 Corinthians 2:14 although we are still incapable of seeing as well as we'd like;
1 Corinthians 13:12.
For example God has always existed, no beginning, no end. Before there was anything created, there was God. We have truied to explain this recently to our daughter in Scripture and devotions and the look on here face of being mind blown was awesome. She is only 7 by the way. Many simply accept the things of Scripture as stated, they believe the revelation of God knowing that it does not need to fit into our logic nor do they believe they must rescue God from His glory of being a Just God who will punish sin eternally.
Others cannot accept things in this way, how God has revealed Himself plainly when it goes against their logic or presuppositions, i.e. that He will torment evil with an everlasting torment, so they attempt to justify God and get Him off the hook because of what they want to believe about Him. This is why we see an inconsistency in their hermeneutic, and their interpretations must adjust and will remain inconsistent from one passage to another. This is their fallacy in a nutshell.