When a voice spoke from heaven in John 12, what did some in the crowd say had happened?

Answer: It had thundered

After the voice said, "I have glorified it," some said it had thundered and others said an angel had spoken.

“Father, glorify Your name!” Then a voice came from heaven: “I have glorified it, and I will glorify it again.” The crowd standing there heard it and said that it had thundered. Others said that an angel had spoken to Him.”— John 12:28-29 (BSB)