Short answer, yes, the WHERE clause could be left out. Thanks for pointing that out.
Long answer: It's usually a bug. The idea is that you are trying to link two tables together, where the 2nd table has a subset of and the where clause is attempting to return only the values that match. But, as written, the question never implied the 3 rows was an issue. Good point.
I found this bug in a query we had been running for years. It is part of our master planning process and was throwing our production numbers off.
The moral of the story is use aliases.