It's the same meaning but a different name from addiction. Gambling fever is automatically addiction because you wouldn't be alright until you have gambled. Same applies to addiction. An addicted person alwwys want to continue gambling, even when he does not have funds to stake for his bet. He does all sorts of things to feed his addiction.
I don't know why some people think "gambling addiction" and "gambling fever" have the same meaning. However, as far as I know, we use similar words in Indonesian, not for health conditions or addictions. I tried to find similar words in other languages, such as "gadget fever" or "bieber fever," etc, which have the same meaning.
So, "gambling fever" means a condition when many people have a strong interest and enthusiasm for gambling, whether it's sports betting, casinos, slots, or lotteries. It's similar to "fomo," when one person wins a maximum amount, and others follow suit to play slots, but it's not limited to just a person, but it can spread entire villages, city or even countries. so in the end, fever is more of a widespread social or cultural phenomenon, where many people flock to a trend or become overly enthusiastic about something at a specific time. something like this mostly only run within few months, till they are gone except addicted person.