That query is used for returning a cartesian product (https://en.wikipedia.org/wiki/Cartesian_product) of both tables.
In this case 100 x 0 equals to 0 rows in total. Similarly 100 x 10 would equal to 1K rows.
The query itself can also be written with:
SELECT Tbl1.* FROM Tbl1 CROSS JOIN Tbl2;
SELECT Tbl1.* FROM Tbl1 INNER JOIN Tbl2 ON 1 = 1;