Mpamaegbu claims to not have provided a link to the source but what actually was the source? If he copied the message from steemit and forgot to put a link, then it can be considered an error. If, on the other hand, he copypasted the post from bitcointalk, then it is blatant plagiarism because his post was not translation nor quotation.
Mpamaegbu will have to answer that question, though I'm not sure it really matters at this point. Whether he says he forgot to reference the steemit article or one of those bitcointalk posts, the result (whatever it may be) is going to be the same.
I tend to believe Mpamaegbu's story about forgetting to cite the source, simply because I'm familiar with him as a member and I know damn well that he knows how seriously plagiarism is taken on the forum, and I seriously doubt he'd take a chance that someone wouldn't discover the source of that post. I've chatted with him via PMs, and he's always been trying to do the right thing as far as I can tell.
This is one of those situations that gets kinda sticky for me. I can voice my personal opinion about what happened, but I definitely don't want to get egg splattered all over my face if I vouch for him and later it turns out that there have been multiple cases of plagiarism. I don't think that's going to be true, and I hope someone can verify that.