Eliteangerous!
You cannot play the game offline, it's not possible, it needs a server.
I classify this as DRM as a side effect.
You are somewhat right, but only somewhat. When you drill down to the explanations from Micheal and David of why online only you get two relevant reasons:
1. "We would have to make an offline version of the galaxy server and we don't want you to have access to that"
2. "We think the core vision (of multiplayer?) would be reduced with a single player offline mode.
The second reason is a rather obvious circular argument. Sure the idea of single player offline is to play single player offline, no doubt about it. It's what I want. If I don't want to be in competition for influence in the galaxy from other players, the argument doesn't hold. It's not unreasonable or surprisingly different from the vision that the game set out to because that is what was promised and what we expected. It's a feeble attempt at a jedi mind trick. I know what I want.
The first reason is rather unclear but basically it's either a "security through obscurity" argument (no datamining and make it slightly harder to create bots (but only very slightly!). The other explanation is that they don't want you to create mods, have fun with the game the way you want to or want to remain control to avoid piracy (DRM!).
All in all I don't accept their explanation. For me it's not about DRM per se but willfully denying the player something out of spite or arrogance.