That’s a good video.
Temperature is important in that beta crystals won’t form or remain when it’s too high, but having the ‘right’ temp doesn’t automatically mean you have beta crystals. Like she said, do a little test, add more un-melted chocolate, or just let it cool and stir for a few minutes more. Cooling and agitation both help with crystallization. Un-tempered chocolate will solidify in the fridge but won’t be as stable.
I’m not usually a fan of silicone molds but I see why most of these recipes suggest them. For a home cook just trying a few bars you don’t have to worry about perfect temper because you can peel the mold off instead of needing the chocolate to contract enough to pop out, like with hard polycarbonate molds. I admit I’ve mostly forgotten the frustrating learning curve part 
