TempDB uses a lot of space in buffer pool
That looks like a data page (page type=1) from a table variable or temp table (negative object id of -1948083318) in the leaf of a clustered index (indexid=1).

From the allocation information and the fact that this does not show up in your second query presumably the underlying object has been dropped. You may be able to get additional information about it, such as original object name, by looking for that allocation unit id in sys.fn_dblog if you're lucky.

If it belongs to a dropped object then one would certainly hope these pages are first candidates for putting on the free list. 

However the article TempDB memory leak? and   associated connect item indicate that there might be a problem in this area...