Can someone explain this blue post to me?

In the post:
“As with Nasz’uro, completion on higher difficulties will include your chances from all uncompleted lower difficulties that week–this also includes the cumulative increase in chances for future weeks.”

Does this mean if you kill it on heroic, there is no point in killing it on normal, it won’t drop? Clear as mud.

i think the wording is like this
example normal 5% heroic 15% if you did heroic you have 20% for it to drop
and if doing normal i think the 5% remains after you did heroic

To clarify my question. If I kill it on heroic, no Fyr’alath drops. Do I still have a chance of it dropping on normal that week?

Yes.

No.

No. Only your highest difficulty matters. The system is basically designed that if you’re killing him on Heroic each week, there’s no reason to also try in Norm/LFR.

(Though I’m unsure if Mythic counts since it’s 100% Drop there)