The bonus was an incentive, which you clearly didn't care about because: a) you forgot about it, and b) you referred your friend who you would have referred anyway
Making it "public" now is just vindictive. If you forgetting about your own bonus for months, and then another month after leaving the company still leaves you eligible for said non-contractual bonus, then what _is_ the statute of limitations? Would you email them 10 years later and ask for the bonus?
If Steve Jobs promised you a company trip to Hawaii if you got the Macintosh shipped on time, and EVERYONE forgot and didn't care, or Steve took everyone out for sushi instead, would you email Apple inc. tomorrow and insist they send you to Hawaii??