Nearly half of all adults in the US (more or less in other countries) have HSV1, which rarely can cause Bell's palsy. The source of infection usually isn't known. Don't obsess about it; you'll never know and it doesn't matter.
No I don't but I'm curious to where he could have caught it from? Is it something I should be worried about?
No need unless you're having symptoms that suggest you have oral herpes yourself.