NM does indeed use the ifcfg files in network-scripts and wi-fi is handled much better through NM than network.service shell scripts so this advice is not that useful.
Back to the OP's issue it is indeed BOOTPROTO none required to disable dhcp.
I'm curious if he reloaded NM after changing this.
A better way overall is to use nmcli to change it at the terminal.
From my notes here:
nmcli conection modify <connection-name> connection.autoconnect yes ipv4.method manual ipv4.addr "10.0.0.1/24" ipv4.dns "10.0.1.1, 10.0.1.2" ipv4.gateway 10.0.0.254
Obviously replace the IP addresses and so on as required.
This has the benefit as well of changing the current and the persistent configuration at the same time.