Must you fight in the fight phase

Had an interesting situation.  I was in melee with a vehicle, I charged it on my turn and brought it down to 2 wounds.  On my opponents turn he of course attacked with it, but I did not want to attack it in his turn because it might explode.  The rules only seem to say that a unit within 1" of the enemy may be chosen to fight not that it must.  I wanted to be able to shoot it to death with my troops out of harms way.

What are peoples thoughts? Is this cheezy, and is my interpretation wrong?

Im fairly certain there was a discussion on this a week or two ago. I'll see if I can find it but I'm fairly certain that their conclusion is that everyone in melee must fight if possible. The "choosing" is in reference to players taking turns for combat.

The FAQ. All models That are able to fight must do so. The FAQ is more wordy

So where is this FAQ?

Was on the 40k FB page. Not sure where GW puts it on their website?

Its under Developer's Commentary on the Warhammer Community page the day of launch

The designers commentary is on this page: https://www.warhammer-community.com/2017/06/17/new-edition-now-available-read-the-rules-get-the-t-shirtgw-homepage-post-1/