What is Online Gambling?

No.
The Premium Fusion Ticket is worth 500 NX. That is not a cash value. You cannot buy it for 50 cents.
You can get 500 NX by paying 50 cents, or by doing an online survey, or by doing an in-game quest, or just because Nexon decided to credit it to your account because they like you (or because they messed up bad).

Again, the only part where you give Nexon money is where you buy the NX. What you do with the NX afterwards is immaterial.

Hypothetical:
I buy a Gachapon ticket for 1000 NX. I use it and receive a Premium Fusion Ticket that can be obtained with much more ease and for a much lower price. So low in fact, that I could have bought two of them. In fact, if I actually wanted one, I would have just directly purchased one instead of using Gachapon. Therefore, if I am purchasing a Gachapon ticket, I do not desire a Premium Fusion ticket. This means that obtaining a Premium Fusion ticket is actually a complete, full loss, with a 50% consolation.

I can get 500 NX by paying 50 cents...or, rather, by paying the preset amount, meaning I'd often be buying more than I actually wanted to (and don't think this isn't intentionally designed!). Or yeah, you can do an online survey, doing probably three dollars worth of labor for a payment of forty cents. I'd love to see what in-game quests there are that award players with NX cash. Same for these mythical cases of altruistic gift credits. And in the case of "they messed up bad", that's usually because, while they do have a limitation of liability, that still requires them to refund "THE LESSER OF TWENTY U.S. DOLLARS OR THE TOTAL CUMULATIVE AMOUNT PAID [...] TO OBTAIN CASH ITEMS".