The instantaneous current (not current flow) is the derivative of the charge flow, q = 50+t, with respect to time. The derivative is 1, so the instantaneous current (not current flow) is 1 amp.
I believe you are confusing the terms. This equation relates to charge on a capacitor. This C is capacitance in farads and Q is the charge. It is not the same as the charge C (coulombs) in your first equation.
Look at it this way. Current is charge per unit time, and has units of coulumbs/seconds or, equivalently, amps. So, for the equation q(t)=50 + t, the only term on the right side that contributes to current is the second term. The first is just a constant. It shows that 50 coulumbs of charge was present in the component to start with, but the component is accumulating charge at the rate of "t" coulumbs per second. So, at t=1 second, the component accumulates 1 more coulumb of charge, at t=2 seconds, it accumulates 2 coulumbs, etc. One coulumb per second is 1 amp.