How have you determined that it was directly attributable to Obamacare, rather than your standard yearly rate increase?
Generally speaking, increasing the quantity of services that must be supplied while increasing demand by threatening fines for those that do not purchase said services will increase the cost of said services.
He never said his benefits changed at all. Assuming he's on his parents' group plan, it's likely that it renewed in late 2013 to avoid Obamacare for one more year (and thanks to a recent decision, this will be allowed through 2016). If this is the case, then the rate increase or decrease would have nothing to do with Obamacare.