Incorrect Test Vectors for AES' MixColumns?
No, $03 + 02 + 01 + 01 = 01$

The problem is that you are misinterpreting $+$, it's not addition modulo 256; instead, it's the addition operation in the field $GF(2^8)$, which can be computed by performing the exclusive-or on the inputs.

And, $03 \oplus 02 \oplus 01 \oplus 01 = 01$