Thats true.
PHB clearly states on Page 114, Sidebox "Spellbook":
[....] Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if its of a level for which you have spell slots and if you can spare the time to decypher and copy it. [...]
And multiclassing gives you higher spellslots than those you would get from your Wizard level.
The section you cite is about the question what classes learn during levelup. But Wizards can also copy spells from scrolls.
