Here when you run this query in XMLA query window it will give error
Executing the query ...
The 'Backup' element at line 15, column 76 ('http://schemas.microsoft.com/analysisservices/2003/engine' namespace) appears more than once under Envelope/Body/Execute/Command.
so we need to run it in batch. In batch we can run multiple XMLA query. But since this is backup we can not run it in transaction. So we have to specify transaction as false in the query