Difference between freqz vs freqresp in scipy?
The equation of the filter is given as 

$$H(z) = 0.2 + 0.8z^{-1}$$

This can be equivalently described with positive powers of z as:

$$H(z) = \frac{0.2z+0.8}{z}$$

The two equations above are mathematically equivalent. The function freqz specifies that the numerator and denominator polynomials are to be entered in decreasing (negative) powers of z, while freqresp specifies that they are to be entered in positive powers of z. So the OP should use the first form for freqz and the second form for freqresp. In contrast the OP has flipped the order which is the not the same filter.

In general, in order for the filter to be causal, if expressed in positive powers of z it is implied that it also must be divided by poles at the origin, in this case multiplied by $z^{-1}$.

Doing the following will result in the same answer as the result with freqz:

dlti = scipy.signal.dlti(filter_coef, [1,0]) # accounting for positive power convention


Flipping the coefficients, as the OP has done, is the "reverse filter". The reverse filter has the same magnitude response but has zeros at the reciprocal locations on the z-plane, given by $H(z^{-1})$, giving the result that the OP achieved.