I think the “ten days” explanation has the merit of being charitable, because it implies that Brendan Eich wouldn’t have made such short-sighted design choices under more favorable circumstances.
(I do not believe that it’s a “sensible principle” to treat text as such a fundamental form of data that a basic language feature like the equality operator should be entirely shaped around it. Surely the consequences of building an entire language around text manipulation should be apparent by considering how awkward Posix-style shells are for any nontrivial scripts.)