Were the Gentiles in Acts 10 speaking to God when they spoke in tongues?
No. The Gentiles in Acts 10 were speaking to fellow men, not to God. They spoke in known languages and magnified God in the presence of the seven Jews and the household of Cornelius, with no unknown tongue or guttural sound involved.
Les explains that when the Holy Spirit was poured out on the Gentiles in Acts 10, the Jewish believers who came with Peter knew it because they heard the Gentiles speaking with known languages and magnifying God. Les asks whether they were talking to God, and answers no; they were talking to fellow men and magnifying God in the presence of these seven Jews, as well as the members of Cornelius's household. There was no manifestation of an unknown language or a guttural sound here. It was speaking languages. This was the second time the Holy Spirit was manifested by giving the gift of speaking more language than what they were normally living with; the first was to Jews in Acts 2, the second to a whole house of Gentiles, and the third would be in Acts 19 to another unique little group.
For they heard them speak with tongues, and magnify God. Then answered Peter,
More Questions
What did the Gentiles' speaking in tongues and magnifying God prove to the Jewish believers?
Hearing the Gentiles speak with tongues and magnify God proved to the Jewish believers that God was doing something they had not thought possible: saving a Gentile without making him a proselyte.