And to understand the back story you have to listen to the founder/CEO speak. https://www.linkedin.com/in/rahulvohra/
He's very charismatic - has a fabulous radio voice and when he speaks you feel like you need to listen. He does alot of podcasts and I get the impression he speaks to alot of the most influential people in Silicon Valley (conjecture). So lots of influential people are pulled into the orbit of what he talks about, which is Superhuman of course, and also the way he goes about business.
I'm not saying anything here except that I think highly charismatic leaders are able to generate a large amount of interest in what they are doing - they speak, people listen and want to hear more, and buy what they are selling. That's why if you pay much attention to the tech scene, you'll have heard about Superhuman from a number of sources in recent times, and you'll read articles like this one that are very positive. If you are highly charismatic then people want you to know you, be around you, hear you and give you what you want.
Paul Graham believes that the person who wins the U.S. election tends to be the most charismatic http://www.paulgraham.com/charisma.html and I think that's exactly true as well of getting funding, and generating buzz for your company/product.
Unfortunately if you're not born with the voice, the ability to listen or the X factor that gives you that charisma, then you're going to have to develop that success and interest some other way.
Of course it's not only about the founder charisma, the product must also be there - and if you've got both then you're probably, well, Superhuman.