It's partially a linguistics issue. If your definition of "tone" is "the way the gear itself changes the signal fed into it" then no, "tone" is not in the fingers. But if your definition of "tone" is "the end result of the sound you attribute to the 'guitar part'" then "tone" is anywhere from partially to mostly in the fingers depending on the kinds of rings you're talking about, which I'll go into more detail about in just a second.
In my opinion, for that reason, the phrase "tone is in the fingers" is kind of a confusing and ultimately useless axiom which only really breeds misunderstandings like "oh so you're saying I can make a Twin on 1 sound like a fully gained out 5150 on 10 because 'tone is in the fingers' huh."
The other confusing thing about saying "the tone is in the fingers" is that the truth of it changes massively depending on how much gain you use. For example if you're using a 5150 with the gain cranked, the only thing your fingers are really going to be able to meaningfully do is play the notes as clearly and controlled as possible while your other fingers mute the strings that aren't supposed to be ringing. Don't misunderstand, that itself is no small or easily attained skill, but still, most any seasoned heavy guitar player is going to achieve roughly the same sound through a rig like that. But if you're playing an AC30 set just on the edge of breakup where the system is so sensitive that you can practically hear yourself blinking through the speakers, then the nuances of any given player will be vastly more influential on what comes out of the speakers. In that situation, any two musicians are going to sound much more like they're playing through two entirely different rigs than musicians in the high gain scenario I mentioned above, and that is exactly the kind of scenario where "tone is in the fingers" is truest in the most straightforward sense.