What does (sol) in a chemical equation mean?
The state (sol) or (solv.) stands for "solvated". Since you are dissolving $\ce{HF}$ in liquid $\ce{SbF5}$, there is no water in that system (which would cause hydrolysis). So it is not correct to use (aq), since it is a nonaqueous system.

Here are some other examples:


Autoprotolysis of liquid ammonia:
$$\ce{2NH3 (l) &lt;=&gt; NH4+ (sol) + NH2- (sol)}$$
Autoprotolysis of nitrosyl chloride:
$$\ce{NOCl (l) &lt;=&gt;  NO+ (sol) + Cl- (sol)}$$
Dissolving sodium metal in liquid ammonia creates solvated electrons:
$$\ce{Na (s) &lt;=&gt;  Na+ (sol) + e- (sol)}$$