It certainly has some close similarities to an assembly language, but I'm going to argue that that's not what it really is.
In an assembly language, the operations mostly map 1-to-1 to CPU instructions. There are some exceptions, such as macros and pseudo-ops (like, say, a CLEAR instruction that really XORs a register with itself); the real point is that an assembly program exactly determines the CPU instructions to be generated. (That's the fundamental difference between an assembly language and a higher-level language like C; in the latter, programs specify behavior).
The calculator undoubtedly has a CPU in it, but I doubt that individual CPU instructions refer to the X, Y, Z, and T "registers", or perform high-level operations like
ПРГ, whatever that means!).
Instead, I'm sure that many or most of the visible operations are done as subroutine calls. And for each operation executed, there must be a significant amount of extra work done to display the result.
You can think of the visible operations as an assembly language for a high-level virtual machine, but that virtual machine is implemented via something like an interpreter running on the real CPU.
Still, I'd say that the answer to the second part of your question:
Did I have a basic idea of assembly languages using this device?