Good idea. I think the StreetComplete developers are German. In Germany food waste and garden waste are collected together (recycling:type=green_waste), so they probably think of it as the same. This also explains why the StreetComplete icon for garden waste shows an apple and a twig, which doesn't make sense in the UK, and selecting garden waste tags recycling:type=green_waste, when in the UK at least it should tag recycling:type=garden_waste...