Lev Weksler is a total fraud. I carefully examined all his videos, and none of them are real. I don't believe he even knows how to properly play the bass, has ever performed in public even in an amateur orchestra, or ever taught a student. Certainly he's literally the only online classical "bassist" I've ever seen who has zero evidence of actual live performances or any other credentials such as a school they attend or teach at or orchestra they play in or whatever.
First, the sound is mostly from a MIDI keyboard, not a real bass. In a few later cases when he tried to "prove" that he was real, he switched to using what sounded like some student player of dubious quality. (I can only guess he may have stolen someone else's recital recording to use as his soundtrack and mime to.)
Second, if you slow down the video (YouTube has handy controls to do this), it's easy to see that he's on the wrong strings, going down when he should be going up, that the bowings would never make anything like the articulation or dynamics we hear (which mostly don't sound like a real bass anyway), he's not at all in sync, the fingers aren't in the right place to make the pitches we hear, etc.
He spent considerable effort deleting critical comments, protesting his innocence, trying to "prove" he's real (by posting yet more fake videos), etc., to continue convincing his adoring young fans of his greatness, then largely stopped posting "virtuoso bass videos" about the time YouTube disabled direct messaging. In short, not only were the videos themselves fake, but his behavior in comments etc. was nothing like any actual busy professional musician I've ever met or heard of.
Nahre Sol's latest PBS SoundField video (on Editing in Classical Music) has a section where they do a blind test to see if they can tell the difference between a real recording and a sample library (which is presumably played on a MIDI keyboard or programmed on a computer). They do quite poorly, even misidentifying their own instruments.
Also, the most popular YouTube video of Beethoven's Moonlight Sonata (with around 170 million views and counting) is a programmed MIDI track, and almost nobody notices...