well by that argument, fuel could be considered as part of "supplies" as well.
Perhaps he has something in mind in which fuel has a special role on the strategic level where supplies isn't?
Heheh, you certainly could
But there are significant differences between fuel and munitions which in my mind warrant one but not the other being separate.
For one, fuel is concerned with hyperspace movement only, and its consumption isn't related to combat or in-system movement. So, fuel determines how far you can go, while supplies determine how long you can stay on the field. Munitions (without additional mechanics), would introduce an additional layer of "how much you can fight" depending on weapons you have. Except that supplies, being used for repairs, also play that role. You could break it down further into "how much damage taken you can repair" (supplies) vs "how much you can fight" (munitions). That, to me, is getting too fine-grained.
Also, fuel adds a higher level strategic concern - movement among star systems - and, since that part isn't implemented yet, there's plenty of room to give it an even more meaningful role without retrofitting existing mechanics.