Here is another passage which seems to indicate that the Old Testament was available in Greek.

"And he went into the synagogue, and spake boldly for the space of three months, disputing and persuading the things concerning the kingdom of God. But when divers were hardened, and believed not, but spake evil of that way before the multitude, he departed from them, and separated the disciples, disputing daily in the school of one Tyrannus. And this continued by the space of two years; so that all they which dwelt in Asia heard the word of the Lord Jesus, both Jews and Greeks." (Acts 19:8-10).

Notice that Paul is in a Gentile building, speaking to Jews but mainly to Gentiles, so that a whole Gentile provience hears to the Word of the Lord Jesus.

Hearing the Word of the Lord Jesus requires the Old Testament, or at least, quotations from it. Jesus Himself said, "Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil." (Matthew 5:17).

For example, in teaching the Gentiles that Jesus is the Saviour from sin... what is sin? Surely the Old Testament must be used to identify what sin is. Were the Gentiles learning Hebrew? It is far more consistent with the Bible and with the known evidence today to believe that the Greek Old Testament already existed, dispersed through the Greek world, the same being the LXX.