Apple Watch Ultra low electric shock

Almost certainly this was pure coincidence and you have experienced an electrostatic discharge. Unless you had your fingers into mains powered electrical equipment or wiring (bad idea) there is no source for electricity which is strong enough to shock, so anything you might feel was a static discharge.

It is extremely unlikely your use of any function on your iPhone could cause any kind of electric shock. Both your Watch and your iPhone have very low voltage batteries which are completely enclosed in the device body and can't cause a shock. Bluetooth and WiFi run continuously on your Apple Watch just as they do on your iPhone so they would not be doing anything different at the moment you felt a shock.

Thank you for participating in the Apple Support Community.

We want to make sure you reach the right team for help with your device. We recommend that you contact Apple Support directly. Depending on your region, you might be able to contact them here: Get Support.