I was also at Burning Man 2013 (when this seems to have taken place), and some of my female friends were approached by middle aged men who offered them massages. When trying to decline politely, these men used a sort of "uptight-shaming" tactic, saying things like "you're at burning man, you need to relax". They ended up going along with it and felt very badly about it afterwards. I'm not saying this is typical, but it does occur.