Sure, but t-shirt and jeans is also what everyone working at an Apple Store wears. It'd be one thing if they didn't say what to wear - then I'd totally understand going a bit above, but if they specifically put in "not formal", then it seems reasonable to assume they mean "match the uniform generally".
They didn’t say what to wear, they said a vague what not to wear. Almost all interviews at that point in time expected attire a step above your intended position. I personally think it was just a silly test of whether you already know what they expect. “You are a great hire but you dressed too nicely for the interview” is certainly a thing that I chuckle at.
