True. The players can wear what they want. Rules however prevent druid characters from wearing metal armour.
Where? Not one word in the druid section prevents such a thing. There is no "can't" with regard to metal armor.
You're massively misinterpreting the sage advice. Crawford at no point says it is not a rule, they merely explain why it is a rule.
Let's see...
"Well, not actually.
Druids have a taboo against wearing metal armor and wielding a metal shield. The taboo has been
part of the class’s story since the class first appeared in Eldritch Wizardry (1976) and the original Player’s Handbook (1978).
The idea is that druids prefer to be protected by animal skins, wood, and other natural materials that aren’t the worked metal that is associated with civilization. Druids don’t lack the ability to wear metal armor.
They choose not to wear it. This choice is part of their identity as a mystical order.
Think of it in these terms: a vegetarian can eat meat, but chooses not to.
A druid typically wears leather, studded leather, or hide armor, and
if a druid comes across scale mail made of a material other than metal, the druid might wear it. If you feel strongly about your druid breaking the taboo and donning metal, talk to your DM. Each class has story elements mixed with its game features; the two types of design go hand in hand in D&D, and the story parts are stronger in some classes than in others.
Druids and paladins have an especially strong dose of story in their design. If you want to depart from your class’s story, your DM has the final say on how far you can go and still be considered a member of the class. As long as you abide by your character’s proficiencies, you’re not going to break anything in the game system, but you might undermine the story and the world being created in your campaign."
So the first bolded part says taboo, not rule. A taboo is not a rule. The second bolded part clearly says it's part of the class story. Story = lore. The third bolded part says very clearly that it's a preference to wear non-metal armor. A preference is a choice, not a rule. The fourth bolded part flat out tells you that it's a choice, which means that it is not a requirement and nothing prevents the druid from putting it on. I've known vegetarians to occasionally break that taboo, so the fifth bolded portion also indicates that it can be broken. The sixth bolded portion literally says the druid can wear metal armor. The sixth bolded portion also clearly says this is a lore feature of the class by literally equating it to story. It also says that a DM could take away the class if he wanted to, but that's not in question. A draconian DM could always do that. DMs can create whatever house rules they want.
At no point, though, is it ever a rule. It's lore and story, not rule. The DM has to enact a rule in order to remove the class.