As a lawyer hired by the players, I would say that : « you can use this variant » is an option, a possibility, and not a restraint or an order. so my client can still roll stats!I was surprised reading it.
The default is using rolls with the player being able to decide to use the default array.
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The variant rule at the DMs option is using point buy. This seems similar to the encumbrance option:
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At no point is the standard array forced by the DM mentioned as being a thing though.
(Pedantically, the way it says "you can" for the point buy, does RAW always want rolling to be available to the players?)