I play 1-2 tables sometimes before I add more, and I'm a 13/10 nitty tag running 10BB/100+. But when I only play 1 table does that mean I'm a donk?
And if you don't have a HUD I strongly suggest gettng one. It will help with assigning ranges. You'll also find that not all multitablers are the 'standard ABC type'. Alot of them are just as bad as others playing 1 table. For example, I know of a player in my database that is 15/0/.7 over 650 hands. That's right, he hasn't raised once at all in over 600 hands, and he's playing multiple tables. That's not 'standard' poker.

IMO counting the number of tables someone plays is no where near as accurate as taking notes on what hands they play from different positions. That is the easiest way to define someones range, just write down what hands they play and how the play them.