The guy speaks about apostates at about the 4 minute mark and claims if one leaves the Christian faith then he does not know if that person was ever really saved to begin with. Their walking away reveals something he could not see, that being, they are backsliden but still saved or they were never really saved.
1) I am not familiar where the Bible teaches the idea of backsliden person who remained saved (Jer 2:19; 3:22; 8:5). The Hebrew epistle is a warning to Hebrew converts about leaving Christianity and backsliding into Judaism again. Nothing indicates they will still be saved by leaving Christianity and backsliding into Judaism for the context of Hebrews indicates they would become lost due to that backsliding...."
Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief." Heb 4:11. Backsliding leads to loss of salvation due to falling as a result of unbelief.
2)
apostate - apostasia
from Biblehub.com: 646 apostasía (from
868 /aphístēmi, "leave, depart," which is derived from
575 /apó, "away from" and
2476 /histémi, "stand") – properly, departure (implying
desertion);
apostasy – l
iterally, "a leaving, from a previous standing."
Apostasy means a change of position or location. The word fall also carries the idea of change of position or location. If I fall from a tree upon the ground then I left a previous position in the tree to a different position on the ground.
1 Cor 10:12
take heed lest ye fall from Greek pipto
Thayer - descent from a higher place to a lower; to fall out, fall from i.e. shall perish or be lost; fall from a state of uprightness.
So as far as a person leaving the Christian faith indicating they were never really saved:
one cannot leave something they were never part of, I cannot leave a room if I was never in the room. Hence one cannot leave the faith if he was never in the faith. If I was always lost and never saved then I cannot fall from salvation that I never had, I cannot fall from a faith I never possessed. One cannot fall from uprightness if he was never upright.
At least 2 logical conclusions can be drawn from falling
1) one cannot fall from a position they were never in...one cannot fall from a tree he was never in just as one cannot fall grace if he were never in grace.
2) one cannot fall into something they already are in....one cannot fall into condemnation if one already is in condemnation...a fallen person cannot fall for he already is fallen.
In this piece we look at whether people who fall back into sin are lost forever. Or that there is still salvation for them.
www.biblword.net
The above link claims from Heb 6 that backsliding/falling away is only "hypothetical", falling away is not real or actual. Yet the context states speaks of those who already have fallen away; "have fallen away" ESV; "and
then fell away" ASV; "and having fallen away" YLT
The Hebrew writer is not dealing in hypotheticals but actually speaking of those who already have fallen away.