That's 30 people in New Hampshire, which is, like, literally half the population the state. That's impressive.
But all kidding aside, the article you posted, this one: https://www.foxnews.com/media/cnn-reporter-struck-size-pro-trump-rally-bronx-deep-blue-district does not make the claim that 25K people showed up. It reports that the Trump campaign said that there were 25K people there.
Here's the thing- the Biden campaign isn't going to lie about the crowd size. But the Trump campaign will lie to you about it. They'll lie to you about something you can easily prove them wrong about. So, if Trump and his campaign lie to you about simple things like crowd size, what else will they lie to you about?