He keeps on telling negative things to Bitcoin despite of its positive growth
It's experienced growth in price, but not growth in much else. It's really annoying when you have two sides and neither of them has an actual point to make.
he makes those absurd comments while he owns bitcoin, if he really does not like bitcoin because he does not sell all the bitcoins he owns?
Because bad things can have high prices.
Some dotcom companies ended up with absolutely insanely high prices based on almost nothing except for their vague association with the Internet. If you were an early investor in these things, you could say "the price is really dumb" and still not sell all of your stock. The same applies here.
You need to separate the market from the users. The market isn't 100% representative of users' beliefs about the merits of each crypto, it's representative of users' beliefs about what other users believe about the merits of each crypto.