Forum traffic – referral or organic?

I learned that forum traffic is referral but I just wanted to make it sure by asking the pros here. In fact, I have a few more questions to ask since I'm relatively new to the SEO industry.

1. Will the traffic falsely show up as organic traffic in GA?
2. Under what circumstances should forum posting be used as a strategy for link-building? Would you use it if you get
(i) a fresh client with 0 backlinks?
(ii) clients with say, 1k unique visitors per month and a number of target keywords…

Forum traffic – referral or organic?