I agree with Keith regarding that used (or counterfeit) mic. Forget about it.
Let's get back to how YOU are recording.
Why are you recording with the mics in OMNI? You realize that doing that means the mic picks up all the room reflections? Some of these will be out of phase, and unless you are recording in a nice studio room with the appropriate acoustic treatment, it ain't gonna work well!
Then, you are also recording vocals at the same time. Your voice is very soft. The vocal mic is picking up the guitar, too (more phase issues?) so your voice is drowned out.
Recording a nylon string guitar guitar can be trickier than a steel string. Usually you want the mic to be 18-24" away from the guitar so that the sound has a chance to 'bloom'. Experimenting with different placements is always advised - just set up your gear, hit 'record', then try different placements while recording, noting (by speaking on where/how you are in relation to the mic) the placement.
As to that girl's video. Pretty sure she is lipsynching (hence the earbuds she's wearing). The vocal has a reverb on it that is NOT on the guitar. She may be recording the guitar part while lipsynching the vocal - or not,because you can't see her playing fingers
You have remarkable powers of observation as you picked out details that reveals Keiko's lip or guitar playing sync arrangement that fooled me ha! When I moved the mic away the guitar dropped way off but should just be better at adjusting the gain. I never thought the earbuds mean she's lip syncing too, wow! I see the tip of her microphone in lower left, however she could have an overhead boom mic off camera too for her voice. I am at least aware of that phase problem when mics are too close together. I learned that 17 yrs ago when I last used the same mics when I recorded two solo acoustic piano albums, and get rid of it by keeping them on omni. I also keep the high/low filter at a flat line the way it was when I was recording piano as I play both very low and very high notes in my open C tuning. I'm also very fortunate to have a phenomenally quiet room in the far corner of the 131 apt high-rise I live in and having them on omni is no problem with interfering sounds. If you have time take a look at my post #13 to Keith and #18 to Rob, and if you might have any input on that... but fully understand if you don't have time. Thanks very much for your cogent and lucid observations!