Yes your guess right. It is very much similar as taking k=1 in <PERSON>'s first law,i.e.,
F=kma
When <PERSON> discovered his law there was no unit of charge defined at the time. <PERSON> arrived at the law by performing simple experiments. He took a pair of turbo electric materials( materials that charge up while rubbing) and charges them by rubbing them. So both the bodies were equally charged but with opposite polarity (one positively and the negatively). He then calculated the force acting between them, when seperated by a certain distance, with the help of a torsion balance, a device which measures very feeble forces.
He halved the charges on the bodies by making them touch any other conductor so that charge shot distributed equally on both the bodies and thus got halved, then he again measured the force between them seperated by the same distance as previous. 531
Next he halved or doubled the distance and again measured the force. Thus, <PERSON> did not measured the charges on the bodies but he was able to arrive at the law.
But,after arriving at the equation, he could use it to define the unit of charge( since it was not previously defined) just like <PERSON> used his first law to define force(read my answer https://physics.stackexchange.com/a/530555/243233 )
Now you can see that <PERSON> took k as 1 but <PERSON> didn't. Why? In fact <PERSON> actually did it. You can see that in CGS system of units it's value is 1. But in SI system it's value is 9×10^9 .Why SI system adopted this value only.
The fact is that SI system didn't adopt the value, instead they calculated it. Just as <PERSON> used one of his laws to define force(Newton's first law) and then used the definition to find the value of the constant G in his law of Gravitation, SI system used the formula of current I=Q/t to define charge and then used that definition to find the value of k in <PERSON>'s law.( If you have problem over this para then read the answer in the link first).
Now I hope that you understand why it can be used as the definition of charge (in fact, it is used in CGS system). 682