Agree with the others. You don’t need to get bogged down in concepts like this. Particularly this one, because as Chris mentioned, it’s kinda BS.
Dude, you’re 125 lbs. You just need to eat. A lot. You actually weigh what I did when I started lifting weights. I was 5’10 though, so even skinnier than you. So, I can tell you what worked for me, because I think it probably applies to you.
I put on my first 30-40 lbs by really pushing outside of my comfort zone when it came to eating. I started eating much larger meals than I was accustomed to. I ate when I wasn’t hungry. I ate a lot of pasta and rice, a lot of chicken, and I drank a lot of milk. I made relatively healthy food choices, as I wasn’t eating a lot of junk food on top of all that, but I definitely ate a lot more than I wanted to. It worked. I put on some fat, but my metabolism was high, as I assume yours is, and so the fat gains were minimal. Once my weight gains kind of stalled, I stayed around 160 lbs, but started to shed some fat and gain muscle. Basically what we call ‘recomposition’. I didn’t change anything in my diet, I just kept eating the same stuff, similar amounts, while continuing to push myself in the gym. Over a period of time, I got to the point where I was at a pretty lean 160-165. Then, I pushed the calories up again, gained about 10 lbs, and repeated the process of improving to a ‘better’ 170-175. This is essentially what I’ve done over and over again to where I am now, which is a VERY lean 200ish lbs. This year I’ll be pushing up to 210-215, with the expectation that I won’t initially be as lean at that weight, but as I get comfortable with maintaining that weight and eating enough to maintain it, I’ll gradually be a higher quality 210+.
That strategy has worked for me for quite a long time. Because my metabolism is so high, I also tolerate junk food very well now. I can eat as much carbs as I want. Hopefully you’ll be as lucky as me in that regard.