Thunderforce attack bugged? Can someone explain?

[76561198427859458]

Opponent has Reactor Slime, 2 Slime Tokens, and Metal Reflect Slime

Metal Reflect Slime:

Special Summon this card in Defense Position as an Effect Monster (Aqua/WATER/Level 10/ATK 0/DEF 3000). (This card is also still a Trap.) If Summoned this way, this card cannot attack.

So we know for a fact that it's a monster on the field.

I summon Slifer, then I activate ThunderForce attack:

This card's activation and effect cannot be negated. If you control a monster whose original name is "Slifer the Sky Dragon": Destroy as many face-up monsters your opponent controls as possible, then, if you activated this card during your Main Phase, you can apply the following effect.
● Draw cards equal to the number of monsters destroyed by this effect and sent to your opponent's GY, also you can only attack with 1 monster this turn.
You can only activate 1 "Thunderforce Attack" per turn.

We know the tokens don't go to the graveyard, so I won't draw any cards because of them.

But Metal Reflect and Reactor both go to the graveyard. Both are monsters. And I only drew 1 card.

Is it a bug, or is there something I'm missing?

Video:
https://www.youtube.com/watch?v=oEOA7P6Iero

[mimizukari]

Metal Reflect slime is not a monster in the graveyard. You do not draw any for trap monsters/spell monsters/pendulum monsters/etc.

[Zoie Shales]

Metal reflect slime is not a monster in the grave, this is not a bug.

[76561198427859458]

Thanks guys. Stupid me lol, should've thought of that

I have another noob question:

https://steamcommunity.com/app/1449850/discussions/0/3187989286469023865/

[redrocketglare]

It failed to trigger for me when NPC's Sangan and Witch of the Black Forest effects triggered, after they were sent to the graveyard...

Bug, or effect not able to trigger because Sangan/WotBF's effects interrupt the flow of the chain?