Error log: is this website hack?
Hackers use "vulnerability scanners" to look for exploitable websites. What the scanners do is try thousands or URLs searching for known programs with security issues. Those URLs look like they're intended to exploit joomla.
So you should be safe, you could check to see what the error generated was and resolve that. It might be a missing record number or something like that.
I don't think you need to get Exploit Scanner in this case.
Hope that helps!