@Jarhamar, @MilEmE09 I can't believe I have to cut and paste this here in regards to helmets.
From the Dress Instructions:
c.A turban shall be worn by members with ceremonial, mess, service dress. Turbans shall also be worn with occupational and operational dress, subject to the safety and operational considerations noted in sub-paragraph a., above. When engaged in combat operations, operational training or when serving with peacekeeping or multinational contingents, adherents of the Sikh religion shall, when deemed essential, cover their head with a patka or other customary clothing item (see paragraph 21.), over which they shall wear the headdress (including combat helmets) and other items of military equipment as ordered by the commanding officer.
They didn't need to be wearing helmets and my assumption is that the showing of turbans was sort of a priority here.
@Chris Pook, if you look at the images, there were other non turban wearing soldiers in the parade.