That particular DT830 is probably made by E-Sun.
In general my guess would also be that Mastech came up with that design. But that is really just a guess, because the majority of 830's I have seen come from Mastech.
It could also be, again a guess, that this originated from some Chinese government-issued design for some standard multimeter, e.g. to be used in large quantities in education, military or certain applications.