My guess is that one of the large forum companies like VerticalScope or Internet Brands made them an offer. Good for them.
Unfortunately my accountant brain went to deduce a market price. Wintertrekking has 1,715 current members of which only 270 have posted more than 20 posts.
Internet Brands (owned by a venture cap firm KKR) has some 2009 data on Wikipedia: 99.8M gross income, 70% from advertising on 62 Million unique visitors/month. Making gross revenue of $93 CPM. That sounds abnormally high.
If the 270 regular members visit 10 pages every day for half a year (and spend the rest on sites like this), that's 486,000 views. Using the gross revenue target above gives an annual gross revenue of 45K. Internet Brands net income is 12.4% of gross revenue making the estimate of $5,500 for a bottom line. With a cost of capital of 20% you would look at a purchase price of $20,000.
Market price is probably in the $10,000 range.
Well, that was a fun 20 min exercise - back to work.