Twofish MDS multiplication
Each byte act as a polynomial in $\operatorname{GF}(2^8)$

You will multiply the elements of the matrix in (Galois Field) $\operatorname{GF}(2^8)$ and add them in $\operatorname{GF}(2^8)$

here is a link where you can find a wonderful explanation for $\operatorname{GF}(2^8)$