That's a good possibility. Luckily, it's a large capacity tank and I did have the sense to restrict how long I kept the adapter squeezed shut to produce a series of pulsed flushing cycles (I wanted to 'shake things up' to allow a net flow on the hot supply to flush out any 'gunk'.
I suspect the more likely cause for the flow rates to appear more equal was likely a reduction of pressure on the cold supply due to the header tank ball c*ck opening in response to the draw down demand by the hot water tap.