It wasn't the opinion of those at the time, since that teaching was never incorporated in the Confessional documents. Nor has it been understood that way in the centuries since his death. It is a recent, novel idea, similar to some of the Marian doctrines. Maybe Catholics and Presbyterians are getting closer after all.
From the Link:
As to the question why not all men are converted and saved, seeing that God's grace is universal and all men are equally and utterly corrupt, we confess that we cannot answer it. From Scripture we know only this: A man owes his conversion and salvation, not to any lesser guilt or better conduct on his part, but solely to the grace of God. But any man's non-conversion is due to himself alone; it is the result of his obstinate resistance against the converting operation of the Holy Ghost. Hos. 13:9.
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Calvinists solve this mystery, which God has not revealed in His Word, by denying the universality of grace; synergists, by denying that salvation is by grace alone. Both solutions are utterly vicious, since they contradict Scripture and since every poor sinner stands in need of, and must cling to, both the unrestricted universal grace and the unrestricted "by grace alone," lest he despair and perish.
No, Calvinists accept the mystery that is God's reason for His election which is founded on His good pleasure alone. They do not, however, as various semi-Pelagians do, deny that men are elected because Scripture affirms that fact over and over.
Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, To the praise of the glory of his grace, wherein he hath made us accepted in the beloved." -- Ephesians 1:4-6
"But ye believe not, because ye are not of my sheep, as I said unto you." -- John 10:26 "According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
For there is no distinction: since all have sinned and fall short of the glory of God, they are justified by his grace as a gift, through the redemption which is in Christ Jesus, whom God put forward as an expiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins; it was to prove at the present time that he himself is righteous and that he justifies him who has faith in Jesus.