Upvote:5
Unfortunately, the Calvinists in the web forum mentioned are misrepresenting the Calvinist position on Old Testament saints.
Westminster Confession of Faith 11:6 states: "The justification of believers under the Old Testament was, in all these respects, one and the same with the justification of believers under the New Testament." (Westminster Confession of Faith Chapter XI: Of Justification.)
In context, it refers to the fact that justification is according to God's decrees for all the elect on the basis of Christ's death, with numerous additional clarifications. The point is that Christ's blood was equally efficacious for them.
Occasionally, you will hear Calvinist objections to calling a person, "Saint Such and Such," not because they believe it is incorrect, but because they think it can imply that there are special categories of Christians who qualify to be saints, while others are not. This has more to do with objecting to the Roman Catholic view of granting certain Christians sainthood after they die.
To Calvinists, a person who is in Christ by faith is a saint, and prior to the incarnation, there were Old Testament people who were in Christ.