I play both, so I know it well.

The double indentations are the giveaway.

The grooves look too wide.
I've got 2 twelve strings & a mandolin. (It's about 5 feet away as I type this.)
There's only one thick, wound string on a mando.
Also, look at the index finger. There is not a deep groove. Barre chords don't require the tip of the index finger. Gets a little relief, right?
So, I'm thinking guitar strings.

That was more than 50 years ago. Use it or lose it; the calluses aren't permanent. I quit playing acoustic for a few years and played only my Les Paul. Getting back into playing the acoustic was painful at first, but not as painful as beginning with a cheesecutter. I think it was a Truetone from Western Auto.

Played 'This Diamond Ring' for my 8th grade music class. Probably should have been expelled...

I'm amazed to see the prices vintage Kay, Truetone and Harmony guitars are fetching these days.

I still have a nice weighted chess set from the Greenstamps' store I got for my 10th birthday.

..and a Gibson Skylark amp. Thought I was Dave Clark. The Harmony stayed in the closet for 25 years (with Puff the Magic Dragon) until I gave it to my son in law. He still has it. The Skylark is in perfect condition but now has a bad tube. We were all so lucky to have grown up in that era. Especially in the USA. Probably the pinnacle of human evolution.

Back in my playing days, I used to have to tell the doctor to not attempt to draw blood from the fingers in my left hand because the callouses were so thick that they could not get that needle down far enough. I even had a few scoff until they tried it. I just sat there shaking my head. Hell, an active guitarist could probably pick up a red hot coal as long as it was only with the tips of the fingers. Just part of the deal when it comes to playing that guitar. (I played bass for many years as well, so mine were wid.)

I can relate.......

But, that pic has to be from right after he got done playing.
I just played for about 40 minutes last night, I play every day, and my fingertips don't look like that right now.
Probably did last night, though.

a grip strengthening tool and just turn the pressure down and involve just your finger tips. Grip it normally and just use the figer tips to squeeze. Helps in many ways. For me anyway.

can damage you hands...use them gently and for short periods of time.

I get those, too.