Question: We all know how an electric current causes magnetic fields. But when a single electron is flowing through the wire, how is this electron creating the magnetic field or how are electrons responsible for magnetic field around a wire?

Answer: 
In the FLRW model which is used today normal (baryonic) matter and dark matter together add up to matter. It dilutes with the growing radius to the third power (because volume is proportional to radius³). So the ratio matter : dark matter is and was always the same, at least in the plot you showed and the model that was used there.

Edit: Maybe the 5.25 to 5 change John Rennie mentioned comes from matter which has been transformed into radiation with time (the sun for example radiates away 4e26 Watt, which means it converts a little more than 4e9 kg of baryonic matter to photons every second. Dark Matter on the other hand can or at least does not transform into radiation energy like normal matter does inside stars).
I the very early universe there was very little atoms. Atoms are mainly made from exploding stars. I the first pie chart there are less atoms and more photons. This is because that was the initial state and the universe. It was highly fence with photons and neutrinos going in all directions.
They will be more of all materials in the second pie chart. For matter and universe has increased in volume with starts ending and expelling larger atoms. The Higgs field continues to create matter. Its just the ratios that have changed. Its not worth put the photons and neutrinos on the second pie chart. Although there quantity has dramatically increased the ratios now are so much lower that the atom ratio.
More humility learning needs to come before your question about dark matter ratios can be answered.