Conversation about green coffee bean

My doorman swears by it. He is so sure, and said he lost 8lb not doing anything different.

My intuition tells me "that makes no sense". (but to me, anything except healthy eating at a calorie deficit + exercise seems like bull)

Unless you use the caffeine to keep your heart rate up all the time. But I don't want to be an arrogant. When I search however, all sources that come up seem like written on purpose promotional ones.