It's fine honestly. He's a fitness celebrity, isn't he? So obviously fitness is important to him and likely to be important to his wife. And anyone with two brain cells reading will recognise that they have the wealth for childcare help and the knowledge and resources and time to be able to work on their fitness.
I don't especially think 'aww, wow! He's so supportive!' because I'm not arsed either way, but he's proud of her achievements and supporting her publicly which is fine. He doesn't say anywhere that everyone should be able to do the same, that I can see.
I think people who take issue with this might be a little envious/bitter that they aren't in the same shape after three kids, and I say that as someone who did zero fitness related activities during pregnancy and have barely started to work on my fitness again several years later! Doesn't mean we can't celebrate or share people's achievements.
It's a bit daft of him though, he will know a large part of his target audience are mums and that it won't land well to brag about his thin fit wife's health after pregnancy lol. But whatever.