This is simply good strategic business sense on their part.
"Perhaps worried that the sun could set on its long-running relationship with the iPad giant, the Taiwanese multinational will decide by the end of the year whether to move into the solar energy market."
Indeed it is a very old conundrum. At one stage in the sixties the then Hungarian government had a very thriviving trade with West Germany amounting to (if memory serves) about 35% or so of their import/export trade. They chose quite deliberately to diversify for exactly the same reasons as Foxcon may be diversifying now. It makes sense - your best buddy now may "go off with somebody else" leaving you high and dry. I do not for one moment believe that Foxcon are going to bail on Apple any time soon but they would be fools not to reduce their exposure to one company whoever that company might be.