Yes, the project affirms these statements.
Aeroplane modes are designed to turn off the cellular radio - they are a benefit for avoiding communication with the cellular network, however, you can still do network connections in other ways such as WiFi even with Aeroplane mode on.
You shouldn't just rely on a single option. It's up to the user to connect to networks that they trust, the services they trust and use features GrapheneOS already provides in regards to that.
GrapheneOS provides features to disable Wi-Fi and Bluetooth to after a set time of no connections, disabling new USB accessories when locked, and more. The OS reduces attack surface in several components.
If a user needed to use the cellular network, there is also an LTE only mode to reduce attack surface by not using legacy 2G/3G code and bleeding edge 5G code.
https://grapheneos.org/features#attack-surface-reduction