I'm interested. When people say losing weight causes the metabolism to slow down, are they simply referring to the BMR going down as a result of the new weight/

I'm interested. When people say losing weight causes the metabolism to slow down, are they simply referring to the BMR going down as a result of the new weight/height/sex combination. Between 65kg and 60kg of body mass, my BMR would go down about 50 calories, which given lifestyle and eating changes, wouldn't be such an issue. Or is there something else I'm missing? How drastically does metabolism slow down? Has anybody calculated how much it does this by, or is there too many variables at play for any accuracy?