Tried doing a search on here and couldn't find it.

Does a unit the fires as a result of Standby have to target the unit that triggered the stanby or can you shoot and an alternate target?

After re-reading the Standby section of the rules reference, I see nothing that requires a unit performing a Standby to attack the unit that triggered the Standby. I think the spirit of the action implies/assumes you're attacking the unit that triggered it, but nothing specifically says you must attack that unit.

No, when you spend a standby token you just perform a move or attack. It does not matter which enemy unit triggered being able to spend the token.