Correct, an additional ordinance was needed to complete the baptism of the Holy Spirit (aka the Gift of the Holy Ghost).
Verse 16 in the OP indicates that they had been baptized in the name of Jesus and had not received the Holy Ghost, so clearly something was lacking. Once what was lacking was supplied, they received the Holy Ghost.
- The apostles were frauds in claiming that their actions could extend this gift to the people they administered to OR
- The laying on of hands (and praying for/over them) was what was lacking
I'll go with option 2 (so did Luke). Once the apostles performed the laying on of hands, the Holy Ghost was given.
Paul in Ephesus
We see the same principals reinforced in Acts 19:
2 He said unto them, Have ye received the Holy Ghost since ye
believed? And they said unto him, We have not so much as heard whether
there be any Holy Ghost.
3 And he said unto them, Unto what then were ye baptized? And they
said, Unto John’s baptism.
4 Then said Paul, John verily baptized with the baptism of
repentance, saying unto the people, that they should believe on him
which should come after him, that is, on Christ Jesus.
5 When they heard this, they were baptized in the name of the Lord
6 And when Paul had laid his hands upon them, the Holy Ghost came on
In this case, they had not received the the baptism of the Holy Spirit, and Paul corrects several things that were lacking:
- They didn't know that there was a Holy Ghost. Paul taught them, but this did not give them the Holy Ghost.
- They appear not to have grasped what exactly John's baptism meant or what covenant they were making, so they were baptized again--in the name of Jesus. But this did not give them the Holy Ghost yet either.
- Paul laid his hands upon them, and then they received the Holy Ghost.
John the Baptist
Although it is unclear if/when John performed baptisms in the name of Jesus, or in the name of the Messiah, or in another name, John is clear that the baptisms he performs do not provide the baptism of the Holy Ghost (e.g. Matt. 3:11)
In all 3 cases, water baptism was insufficient to receive the baptism of the Holy Ghost. A separate ordinance was needed. In no case is it stated that the receipt of the Holy Ghost came immediately upon the performance of the ordinance of the laying on of hands, but in each case an ordinance was needed (see John 20:22 to this effect as well).
Was placing their hands on them a necessary condition to receive the Holy Spirit?
I don't know if elbows might work too=), but clearly an authorized ordinance was needed in order to complete the baptism of the Holy Spirit.