Re:
I'm not 100% certain about this but browser pre-rendering combined with autologin might give the impression of the guy logging in to the site without him actually doing so himself. (In plainer English: browsers can preload parts of webpages, in the background and unknown to the user, before the user even clicks on a link to the site. It gives the user the impression of speedier performance when the link is clicked on.) If he has a Retrobike link on his home page, the browser might well pre-render parts of it. Whether that would include autologin is the part I'm not sure about. Nevertheless, in theory, someone else viewing his homepage could be sufficient to give the impression he'd logged in.
I wouldn't go looking for the knuckle-dusters or calling Interpol just yet then. Given that LongboardSi hasn't posted since August 2nd, I'd be concerned rather than outraged at the moment. And for a tenner's worth of bits? If he wanted to defraud someone, he could have got a better stash than that.