You are correct, a filter mounted face up under an engine doesn’t need an anti drain valve; it will naturally remain full. The valve is only there to prevent oil draining out of the filter to the sump, where a filter is mounted horizontally.
Afaik the NC doesn’t have hydraulic tappets so that is not the issue. Its more likely that NC start up rattle would be VVC related. I am not disputing that the filter stays full but rather questioning whether the oil in the passages downstream of the filter and above it in height can backflow thus needing to be refilled when the engine is started.
Without the drain back valve the oil runs back into the filter and makes the top of the filter the highest point of oil (assuming no siphon effect into the sump). With a drain back valve the oil should stay as high in the engine as the first outlet after the filter.
In all probability the oil is flowing enough to eliminate this difference whilst cranking before it’s even fired up