Your neighbor is certifiable idiot and should never be allowed to breed as he will breed more morons
What your idiot neighbor is not taking into consideration is the coefficient of expansion per degree when mixing different types of materials
About ground differently domestic cast iron is the way to go.
Cast iron below ground is also my preferred choice of materials as long as i conditions allow
Even Charlotte pipe that makes cast Iron and plastic piping suggests for a safer quieter system cast iron is the better choice
Go to any plumbing supply and ask to see a 2" cast iron sweep and a 2" PVC ell and then think which one is easier to snake, which one offers a quieter system which one is is safer in case of a fire?
If you need to save money then by all means use cast iron for waste and soil lines and plastic for venting.
One day look up green peace and then see PVC .