caf -- When essay previously mentioned this I forgot to respond directly. So, now...
Jesus said, "Therefore I say to you, any sin and blasphemy shall be forgiven people, but blasphemy against the Spirit shall not be forgiven. " Whoever speaks a word against the Son of Man, it shall be forgiven him; but whoever speaks against the Holy Spirit, it shall not be forgiven him, either in this age or in the age to come." (Matt 12:31-32 NASU)

What Jesus described here, blasphemy against the Spirit, has sometimes been called "the unpardonable sin." The occasion for the utterance in Matthew was the subborness of the Pharisees, when Jesus power over demons had led people to consider that Jesus might in fact be the Messiah, the Son of David (Matt. 12:22-23). At that time, in response, the Pharisees objected that "This man casts out demons only by Beelzebul the ruler of the demons." Matt 12:24 NASU Mark tells us that this stubborn rejection was the reason for Jesus' statement (Mark 3:28-30). Luke connects the idea of blaspheming the Holy Spirit with the idea of disowning or denying Jesus (Luke 12:8-10). In each case there is a conscious rejection of truth, refusing to accept what is known to be true. Paul discusses a similar idea in 2 Thessalonians 2:9-12 in reference to people who refuse to love the truth and be saved, and delight in wickedness rather than truth. Hebrews talks about this with reference to people who have known the truth and turned away from it, describing the impossibility of restoring one who already knows the right answers, and has experienced the blessings of God, but has rejected them (Hebrews 6:4-8). Peter describes it as "a dog turning to its own vomit" (2 Peter 2:1-22). In each of these passages,it is not merely sin that is being discussed, not even the sin of blasphemy, but the willful rejection of truth. God allows everyone their own sovereign will. The only people truly beyond God's help are those who refuse to accept the truth, those who will not repent.

Was this what the writer of the apocryphal book of Wisdom wrote about in WS 1:6? Not as rendered in the version essay cited. In that version, "anyone who speaks against God" would not to be forgiven. This is quite different than Jesus' teaching that every sin and blasphemy would be (could be) forgiven. It was on that basis that Paul could say "I once was a blasphemer..." (1 Timothy 1:13) but he had been forgiven.

Part of the question though was as to whether there was any Old Testament teaching that provides a backdrop for Jesus' statement, and there is.
Isa 63:7-10
7 I will tell of the kindnesses of the LORD,
the deeds for which he is to be praised,
according to all the LORD has done for us--
yes, the many good things he has done
for the house of Israel,
according to his compassion and many kindnesses.
8 He said, "Surely they are my people,
sons who will not be false to me";
and so he became their Savior.
9 In all their distress he too was distressed,
and the angel of his presence saved them.
In his love and mercy he redeemed them;
he lifted them up and carried them
all the days of old.
10 Yet they rebelled
and grieved his Holy Spirit.
So he turned and became their enemy
and he himself fought against them.
(from New International Version)
See also Psalm 78:8, 40ff, 56ff, 95:7b-11

God showed kindness, showed his power, and gave directions to the generation that crossed the Red Sea, and they, knowing his power and his mercy, and his will, rebelled and grieved the Holy Spirit. Virtually the whole generation died in the wilderness, having made God their enemy. Fifteen centuries later, the Pharisees watched Jesus do good deeds, heard him teach and saw his power, and then attributed his power to the devil, not because they believed it to be true, but because they didn't like or want the truth.

In his trial, Stephen also referred to this concept when warning his accusers not to resist the truth, "You stiff-necked people, with uncircumcised hearts and ears! You are just like your fathers: You always resist the Holy Spirit!" (Acts 7:51 from New International Version)

No, the New Testament teaching about blaspheming the Holy Spirit is not an allusion to the apocryphal WS, and yes, there is a reference for the concept in the Old Testament