They way I read it the banks weren't investing per se, they were financing.
7-year 3.5 billion euro project finance deal
Must admit I've never heard of a broadband network being bought on HP, as it could be harder to inventorise the assets, but why not if there is no starting collateral to use as security for a loan. There's been weirder things bought on tick. Business lending would usually be the cheapest way to finance something like this if you have a proven track record. I'm certain the banks will no doubt cover their own backsides though.