After reading this article, I'm not sure he knew. The timeline and content of the texts, which LE likely has investigated, tell a little different story.
http://www.roanoke.com/news/crime/blacksburg/eisenhauer-texted-pulaski-man-original-plan-failed-before-nicole-lovell/article_f95a880e-14e9-5888-9e98-7af54f78d881.html
The guy said that Eisenhauer had asked him for advice dealing with a girl he met "at a party" who he later found out was underage. DE texted him that the girl didn't want to break it off and he was afraid she would cause problems. The online guy told him to ignore the girl until she moved on.
When that plan - the plan to get NL to stop communicating with him - failed, DE asked him about where "hide a body". The guy thought he was joking and didn't reply. LE didn't arrest him because (we assume) they already had access to the content and time/date of those text messages. Perhaps the SW is to check they guy's phone and computer to make sure there weren't any other messages.
I have a hard time believing anyone would knowingly advise a stranger about how to dispose of a body. A lot of risk with no benefit.
Also strange is that the guy said DE asked him for advice on "how to kiss a girl". Wow, hadn't we wondered before whether DE was a virgin, socially awkward with girls? My theory was that, due to his strict religious upbringing and education, DE developed a weird kink about young girls as a way of dealing with extreme sexual repression. People like DE are schooled to remain virgins until they are married.