Technically, both are gambling. Once there's money at risk for bettors, we can consider that as gambling already regardless of how it was played.

Aside from that, both sports betting and fantasy sports required not just being good at doing analysis (skill-based) but also having good decision-making skills. Although generally, we can't take out the fact that luck also plays a role in both, regardless if the gambling is skill-based or what.

It now depends on the bettor's own preferences on how they define or compared both.