SQL inner query conundrum

I recently suffered through a minor database disaster. The query I meant to run was something like this
Code:delete from table_a where x_id in (select x_id from table_b where field_a = 2345)What I in fact ran was:
Code:delete from table_a where x_id in (select x_id from table_c where field_a = 2345)Now, table_c didn't have a field x_id but instead of exiting with an error all records were deleted from table_c. We were able to recover using backups and transaction logs.

This was run on SQL Server. I verified the behavior substituting 'select count(*)' for delete.

I was shocked by this since my expectation is that the query would fail however I found this on a Microsoft page discussing subqueries:
Quote:

If a column is referenced in a subquery that does not exist in the table referenced by the subquery's FROM clause, but exists in a table referenced by the outer query's FROM clause, the query executes without error. SQL Server implicitly qualifies the column in the subquery with the table name in the outer query.

In the query in question table_a did not have a column named field_a so SQL Server must not only have satisfied the requirement for x_id in the subquery but also ignored the where clause giving
Code:delete from table_a where x_id in (select x_id from table_a)If this is what it does I have to wonder is this an expected SQL Server behavior? A SQL behavior? A bug perhaps?

To me it makes no sense.