How much Alonso had to do with it is unclear, but he would have at least known what the plan was before the race started. I imagine that after his problem in quali, the team would've told him what they planned and what they wanted him to do accordingly, strategy-wise. As has been said already, such an aggressive fuel strategy makes no sense for someone starting so low down - unless they virtually
know an SC period will happen immediately after the first stop, in which case it becomes a brilliant strategy. And with Alonso, they knew they had a driver who would drive well enough and consistently enough to make the most of any brilliant strategy.
My feeling is that the team devised the plan, possibly with Alonso's input, and Alonso then willingly did his bit to execute it.