There's the possibility it's not a bot, doing a search on the name shows it has been joining other forums recently too and posting the same basic crap.
Basically a bot or advertiser in this case which could be a human or at least using a human to get past the sign up phase posts hundreds to thousands of similar links and hopes someone will click on it to either make money from advertising or to simply hijack the system you are using with malicious code. Both are bad form.
A troll is more along the lines of somebody who tries to incite arguments or "flame wars" just for the sake of causing trouble. They say things that aren't correct to irritate users into responding or purposely find topics that are hotly debated and start threads on the topic, and then pick a side and run with it even if they haven't got an idea what it is except for the most vague concept.
In general they try to seem like they have a realistic goal or problem that needs help with but end up spinning loops of circular logic and stupidity for great lengths of time for no reason but to waste other people's time entirely for their entertainment.
The image it's using seems to be well wide spread across the Internet, as in its not unique just a copy of somebody else's copy. It makes sense to use a picture of a woman since statistically people feel more trustful of a woman than a male, and so such an image could and should lead to more clicky clicky on dirty link link.
