There was a known hack - well at least it acted like one - which would allow a user that was not logged on to access the export page template on older versions of dnn.
The url you are seeing is how that hack appeared
On most sites - including your own I would suggest attempting to access that url will force the request to automatically be redirected to the LOGIN page.
IF you check the url on your own site - (add your domain name to the front) - it will take you to your login page.
So in terms of the hack/bot hit - its not likely that you are being effected in any way ...
HOWEVER - it is also a possible precursor for the spambot attack - in that it is ONE of the possible ways that the spambot attack attempts to work out of a site is running DNN.
I would suggest that you looking at upgrading to the latest version of dnn that has solutions in place to deal with that issues as well.
Finally the reason you are seeing an exception when this bot hits your system is a little more complex.
There have been a number of known issues in older versions of dnn - that cause exceptions to happen with a bot or spider or crawler hits a site for the first time - especially if the site is not running a keep alive system.
A lot of those exceptions can be traced back to a serious issue in the way the scheduler used to work - effectively if a crawler makes multiple requests at the same time (something the always pretty much do) the scheduler can be falsely made to launch multiple times - which eventually causes an exception .
The only solution that I am aware of which deals with that issue is an upgrade of dnn to 7.3.3.