Well I just have this feeling that its not Michael. あなた can tell because of how Jason pronounces the words, he says it differently than how Michael would say it. I alson think that his voice is a little bit deeper than Michael's voice.
for me it's not possible to explain how I know. あなた just have to have that gut feeling. like... all us ファン have Michael's voice memorized so we can just tell... there's really no other way to explain it. I can just tell xP