I think he was referring to false conversions. People who sign up for a "get out of hell free" card, with no change, no Spirit led repentance, or bearing fruit.
Once God saves us, he keeps us! But a mental assent in an emotional moment is not being born from above. Now, altar calls do not necessarily always result in false conversions. There may be some, where God uses that moment to truly save them, especially if the Word of God has been preached in power! But it was God who predestined that person to be saved. He initiated the changes, resulting in true repentance from the heart!
It seems like such a shallow and man centered gospel, to think we make the choice, in our evil fallen state to be saved! What could be more prideful and puffed up, than to think an unregenerate person can tell God he wants to be saved! What a mockery of the gospel, to think we are equal partners with God in salvation.
God is sovereign. He does not lose those he has presdestined and chosen to be his adopted children. How could we walk away from God? Where would we go, when God is omnipresent, omniscient and omnipotent? Why would God allow one of his children to walk away? A good parent will not let go of their child who is rebelling! How much more does a good God, who commands the universe know how to draw his own to him, and keep them?
When I lived under the threat I could lose my salvation for any little sin, I was no different than the Canaanites or the Jebusites, with their capricious gods, who couldn't be trusted because if a whim, who were nothing but dead idols. That is what Arminianism is to me! It is trying to appease a distant dead god, by the works of my unredeemed will. I praise the living God that he had me walk away from those false and negative doctrines that kept me in fear and bondage of losing my salvation!
Yet I do believe we need to be walking with God and obeying him every day! But it is God, through the Holy Spirit who gives me both the desire for obedience and the ability to pick up my cross daily and follow him!