Returning value with Clustered index
When you created the clustered index with ename the rows in the table were shuffled to be in that order. When you dropped the index the rows were not reshuffled. 

There is no guarantee that the rows will be returned by a query in the order that they are stored, but often this is what happens. 

If the order is important then you would add an ORDER BY (and would be well advised to cluster the table on that field too to avoid sorting every time).

But don't choose a clustering key just because of that. For a more thorough discussion of clustering and heaps see http://kejser.org/clustered-indexes-vs-heaps/