Go to each VM and go to the tasks and events tab. Click on the events button, then look for the time frame when the ESXi host rebooted and there should be an event that shows the VM being migrated from the rebooted ESXi host to the new host it is on.
I know that is a lot of work, but that is the only way I know of without scripting it.
You could use powercli to look for events within a certain time, from a certain host ...