The first thread from SunnyFlowrr dates back to Jan. 24th, with no photo of the gills.
At this date (with neither photo nor measure), it was not clear what was intended by "small gills", and perhaps the trouble was actually not as severe as now.
With these limited informations, Herpin Man was right when he answered (Jan. 24th) that the gills can expand or contract on a limited basis to adapt to the oxygen demand, either because of variations of oxygen in the water, or variations of the axolotl's needs. When I give a big dinner to my axolotls, they often are more expanded (and more red) gills during the following days, probably because they need a bit more oxygen to digest this food.
But now, it's different. The more recent threads, and particularly the dramatic photo, told us this was a huge problem and not a normal reaction.
Don't overlook the dates when reading the present thread.