I don’t have much to add, Ricky, except that your correspondent sounds like a particular kind of Calvinist: one who realizes the Arminians have a point about Christ having died for all people, but who also realizes the Calvinists are correct that whoever Christ died for we can trust Christ to competently and surely save from their sins.
Thus, Christ has to have died for all people (“the world”) collectively in some way (not only for the “elect”); but also not to have died for all people individually (or else He would save all sinners from sin, and that would be Christian universalism!)
What’s weird is that he doesn’t just take the line of other Calvinists that Christ didn’t die for the whole world but only for the elect (even though His sacrifice was sufficient to save the whole world); thus Christ did not die for all people individually but only for all kinds of people across the world (distributively, as it’s called, not collectively). Or else take the Arminian line that Christ died for the whole world including for all individual sinners collectively, but Christ fails in some cases due to the choices of sinners.
Hopefully someday he’ll take the Pauline line instead, that God was pleased through the blood of the cross to reconcile all things to Himself, things in the heaven as well as things on the earth, the same all things that He created and which depend on Him for continuing existence, all things whatever that need reconciliation to Himself (i.e. all things which have rebelled and so are alienated and hostile in mind toward Him, engaged in evil deeds, whether in the heavens or on the earth, whether thrones or powers or principalities, visible or invisible)–and that if God reconciles and justifies us (the helpless, the ungodly, still sinners) to Himself through the death of His Son, how much moreso, having been reconciled, shall we be saved in His life!
Those God dies for will be surely justified and reconciled; the God Most High upon whom all things depend (in the fullness of deity) was pleased to die for all things in order to reconcile them; sinners are who need to be reconciled, so the all things whom God dies to reconcile to Himself must be all sinners in creation; and if reconciled they shall surely be saved into the life of Christ.
The logic couldn’t get much more direct.