Basic reaction question

[Learnbydoing]

Rhodium's Melatonin to Mexamine synthesis (

https://www.thevespiary.org/rhodium/Rhodium/chemistry/mexamine.html

) involves sodium dithionite, and my question is... why?  The HO- attacks the carbonyl, the electrons get knocked up to the oxygen, then they jump back down and knock the mexamine off.  Even with the amide drawn like it actually would be (what with the double bond to the nitrogen and not the oxygen), the results come out the same.  Is this to avoid NH3->NO3 under the harsh reaction conditions of reflux?  Shouldn't the inert atmosphere take care of that?  I am confused.