In reality, 400 metres of new line added from the old Alex Dock Yard (Regent Road crossing) to Strand Road. At the same time, the existing line was replaced with two crossovers also inserted, so two lines to / from Strand Road straight on to the Bootle / Canada Dock Branch line. The purpose of the work carried out was to give more flexibility and to make it operationally easier for trains to exit and access the mainline. Now before that was carried out, you could still have two trains in and two trains departing the docks within the hour too, so nothing new.
To emphasis the point, a train can be in the four mile section between Bootle Junction and Edge Lane Junction which takes 15/20 minutes to transverse. Once train cleared section, in theory another train is able to enter that section. However, in practice, only happens occasionally as there tends to be only approx 10/12 trains in each direction per day (only on some days though) which would include biomass, intermodal/container, scrap trains and may be the very occasional steel train.
Bottom line, just political spin by the D.o.T to suggest they know what the talking about and they are good servants to the public! If they cannot get that right, what chance with HS2 matters!
(PS I dont blame Peel Holdings making the most of the free publicity as advertising their services and capacity so why not).