isolation transformer - electrocution
there is a potential difference between the wire and the ground,

no. Or rather, it's not fixed. The transformer doesn't connect primary and secondary side on a potential basis.
$$V(t)=230\sin(2\pi50t)$$
is wrong! You need to add a voltage offset,
$$V(t)=230\sin(2\pi50t)+V_0,$$
because the transformer's secondary is floating. That \$V_0\$ could really be anything. However, as soon as anything connects the circuit to ground, a very short (and probably not very high) current flows, bringing the secondary loop to be biased to ground.
So, the person touching the wire defines the ground point, and the rest of the circuit now swings around that. Since there's no voltage difference between hand of person and ground, no current flows.