It's normal for Neymar to play poker, he's been a poker player for many, many years, since he played for the Santos team in Brazil, besides poker, Neymar Jr is also known for being a competitive online video game player... Ronaldo Fenômeno, former Real Madrid and Brazilian national team player, plays alongside him.
I don't know this history of his but since I'm not really into football and didn't know that much on it. But I've known big figures on some sports that I'm not a fan of so this is kind of big deal for those fans that have been following him. I'd agree that it's not something bad at all, it's bad if he's exposing himself and shows how addicted he is but if it's just a typical poker game and he just did it on an important occasion where he's celebrating like for this one, it's for her daughters birthday. I just hope that his fandom won't judge him or be disappointed on him.
He's still a human and he's not different at all as a creature and does things like we do. If we play football or any sport, he's also doing that. If he we play games, we also play games. If we gamble, it's very likely that him and other football stars are also into gambling. So, we shouldn't be judgmental as he's not gambling with our money. He's playing poker with his money that he's worked hard as he dedicated his life into the sport and he'd earned honest money so, it means that he's gambling with his honest and hard earned money.