Trading is not gambling but most traders are trading in a way it is gambling for them and that is why they are losing. Trading is as risky as gambling if you do not understand how it works.
Gambling is based on luck. Trading is based in knowledge, patience and experience.
Many times we expected Real Madrid to win a game or score a lot of goals. So even with knowledge, patience, & experience, we make mistakes and wrong predictions in everything we do. So we can say that the luck factor is important in everything... as you said, not everyone can be on the same side, but we can also say that nobody has a 100% winning rate.
So when someone decides to risk some money on trading to get more money it's gambling. Knowledge, good analytical skills, and being well-informed about developments in the global crypto scene increase the chances of better results, but there is nothing that guarantees profit.