It is possible that it may be a bot but are system attempts to detect bots and removes that click traffic if not deemed to be human traffic. It's possible that a bot can slip through. It may also be possible that some of your links are being shared throughout the web and being picked up by Facebook content aggregators. If you want us to look more closely at a link and it's click traffic, send an email to support [at] budurl [dot[ com and with the link in question and we can investigate.