To me, this sounds entirely plausible. Trying to describe a semiconductor process by a single number is almost as abstract as describing a song with a single number. First of all, the definition of that number is somehow vague. It describes only a single design rule, the gate width of a transistor. But that already assumes a certain fundamental layout of the transitor, which no longer applies in advanced nodes with for example fin fets and all kind of 3d structures. It also does not account for all the many hundred design rules characterizing that process. To compare two processes, you not only need to account for the transistor density, but also the performance characteristics, like energy used, leak currents, switching speeds and so on.

With the 7nm process, TSMC seems to have clearly pulled ahead of Intels 14nm process. The delayed 10nm would be competing with the TSMC 7nm process. The 10nm sound not very advanced, but it hides that other parts of the process were very aggressive in specs. As everyone in the tech industry knows, complex projects can get stuck easily. Sometimes for obvious mistakes, but often hitting a road block, where no one expected one. So for whatever reasons, the 10nm project was quite delayed, we will see in 2019 if they manage to hit the market at their current schedule.

The 7nm project is run independantly from the 10nm process, so it runs on its own time scale. If they are not directly based on each other, it is quite plausible that they made a completely different set of design decisions and thus were not hit by the same road blocks the 10nm process had. As the 7nm process is in an earlier phase of its development, it might of course have just not reached some of the road blocks yet, but it is not necessary that it does run into the same problems as the 10nm one.