Here are the verses you mention: (1 Thes 4:14-17)
We believe that Jesus died and rose again and so
that God will bring with Jesus those who have fallen asleep in him.
15 According to the Lordís own word, we tell you that we
who are still alive, who are left till the coming of the Lord,
will certainly not precede those who have fallen asleep.
16 For the Lord himself will come down from heaven, with
a loud command, with the voice of the archangel and with the trumpet
call of God, and the dead in Christ will rise first.
After that, we who are still alive and are left will be
caught up together with them in the clouds to meet the Lord in the
air. And so we will be with the Lord forever.
Please note the highlighted sections and the order
1. When Jesus returns he will bring with Him those who have died in
Him (born again Christians) for they are with Him in Heaven now. But
they too still await the resurrection of the body to receive their
new spiritual body.
2. The spirit and soul of these believers will then be united with
their new body through this resurrection.
3. Then both those who have been resurrected and those believers who
are alive when the Lord returns will be caught up to meet the Lord
in the air.
So to answer your question specifically, the two groups you mention
are one and the same.
All the best.