If the competition is based on baking a pizza, then photograph quality should not detract from the quality of the entry. If the competition is to bake a pizza and present it with filters, enhancements and AI enhancements then that is a different matter.
It is great to read differing opinions 
Surely the best way to avoid any issues would have been to not allow any form of modification to the images. If it is allowed then some members could take advantage and go beyond just enhancing the colour.
I disagree.
You can't have a level playing field anyway. I mean, if somebody is shooting with a proper DSLR and somebody with a cheap Android, there will always be this advantage. People with good skills in photography as well. I understand the wider perspective of @icopress's decision. Now we have to accept the fact that this is not only about making good pizza but presenting it well in a digital world, there is no way around it.
However, I believe in the judgment of people that they will surely consider this while giving votes.
Obviously, there is a fine distinction between playing within the rules and cheating, which I am sure the manager will take care of.