I'm trying to avoid the use of my isp's nameservers for dns but despite the fact that i've configured 'DNS forwardings' to OpenDNS, my isp is still being used (i think) according to logread:
Although it is not wrong to use in case of unconditional forwarding, it is mostly used when you need to forward DNS queries to a custom port or utilize conditional forwarding.
Upstream resolvers are more convenient to set up relying on network interfaces which typically allows to use interface-specific configurations, e.g. independent IPv4 and IPv6 resolvers or connection-specific resolvers.