It's most definitely not gambling.
If you are referring to mining. even though you can't exactly predict the rewards, you put in the effort needed to get that coin and the outcome depends on your (or rather, your computer's) speed, strength, etc.
When it comes to trading or investing, ideally you make decisions based on rational factors such as news and analysis. Therefore your gains and losses are not completely out of your control like it would be in the case of gambling. Of course, if you don't do your due diligence and make decisions on a whim, you might as well be gambling, but that's not cryptos' fault.