They are not "just as reliant as before", they are only reliant on gas/coal/whatever when the wind is having a dip. It is clearer when you look at the energy consumed in joules: A 114 MW datacenter consumes 114* 10^6 * 3600* 24 Joules per day. The renewable power generator that Google has a contract with commits itself to putting that much Joules into the grid every day. When the wind is out, nonrenewables fill up the slack, and when there are high winds, some of the customers that would have otherwise been supplied from coal plants get wind energy instead.
On average though, 114 MW is pulled out of the grid by the datacenter and 114 MW is put in by the renewable energy company. The rest of the grid, bith producers _and consumers_, act as a battery for when the output of the renewables is either higher or lower than the contracted amount for the datacaenter.