Is 'LEFT OUTER JOIN' equivalent to 'JOIN' in Microsoft SQL

No.

JOIN is equivalent to INNER JOIN.

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Check this example.
Since it returned the rows, we can assume it's an INNER JOIN.

and checking documentation:

INNER
Specifies all matching pairs of rows are returned. Discards unmatched rows from both tables. When no join type is specified, this is the default.

Also, according to this post, the type-part of the JOIN clause is optional:

For instance, the entire type-part of the JOIN clause is optional, in which case the default is INNER if you just specify JOIN.

For instance, the entire type-part of the JOIN clause is optional, in which case the default is INNER if you just specify JOIN.

-Source LEFT JOIN vs. LEFT OUTER JOIN in SQL Server