....but those Jews , Devout men, from every nation I believe were Jews who returned to Jerusalem [from every nation].....
Yes, in order to observe the feast at Pentecost, then they returned home (eventually).
Paul told the Jews, "It was necessary that the word of God should first be spoken to you" (Acts 13:48). The gospel was to 'the Jew first' [Acts 3:26; Ro 1:16]. There was a very serious time line involved for every Jew of 'that generation' alive on the planet. The urgency of the message to 'the Jew first' was 'Save yourselves from this crooked generation' (Acts 2), and 'Every soul that shall not hearken to that prophet, shall be utterly destroyed from among the people' (Acts 3).
Consider what was coming upon 'that generation':
upon you may come all the righteous blood shed on the earth, from the blood of Abel the righteous unto the blood of Zachariah son of Barachiah, whom ye slew between the sanctuary and the altar. Verily I say unto you, All these things shall come upon this generation. Mt 23:35,36
God made sure that every Jew on earth was given the chance to 'hearken to that prophet' before the wrath came. All the Jews of that generation on earth heard the gospel, and were given the chance to repent and escape the wrath that was to come upon 'that generation', and for their progeny to avoid the curses of the OT [Lev 26; Dt 28 & 31,32] that were to come upon the race. God gave her time to repent (a full forty year generation), but she would not