On the face of it, it’s easy to see why you would think that way, but queues are very complicated things.
It clearly states that the numbers listed are average wait times over the last seven days. So firstly, there’s going to be a range in the numbers to arrive at the average. it could be 120 days for the guy who gets his stuff reviewed on Monday, and it could be 136 for the guy on the following Sunday. Secondly… your 150 days isn’t included in the calculation, because it hasn’t been reviewed yet. When it is, then it will be included, but you probably won’t be that bothered by then as your item will have already been reviewed.
I have no reason to doubt that the data used to create that page is correct… but if it says 128 days, then nobody should expect that their item will take exactly 128 days to be reviewed. It’s more of a ‘for your information’ type thing, as it’s impossible to know exactly how long your item will take, especially as there may be thousands of files waiting between your item and the 128 day guys item.