Sometimes we just don't know exactly where some of our bottles come from, but there are a variety of reasons for this.
There are a number of bottlings that don't carry the name of a distillery, often carrying the name of an independent bottler's label instead. It is thought that distilleries like to release some bottles like this, without using the name and therefore using a different marketing strategy. It is also believed that some independent bottlers reach agreements with distilleries to brand the whisky this way also. There is always a lot of guesswork with these undisclosed bottlings, some easier than others to identify.