Should he refer to a kettle from Britain as a foreign kettle? Genuinely, what way of referencing it would have been unobjectionable to you here?

The electric nature of the kettle isn’t what makes it abnormal for Americans (it might not be owned by every household, but people aren’t generally surprised or confused by them), it’s because Britain has 240V and the US has 120V electricity in most outlets, so American electric kettles take longer to boil water.