This is true but it needs perspective, and I am by no means anti-immigrant. I'm actually a pretty open border person, and am 100% against Trump's proposals (though perhaps there are some instances of H1B being abuse [see Disney].) However, this study should have a big caveat, for starters there are significantly more tax benefits for starting a business if you are an immigrant. Secondly, immigrants don't have entrenched interests or preoccupations that would otherwise give them a very high opportunity cost to starting their own business. So the start-up industry is a bit skewed in favor of immigrants naturally.
I would love for us to equal the playing field, not by blocking immigrants, but by leveling the field on tax benefits and subsidies (ideally getting rid of subsidies and flattening the structure) and have reforms that lower the opportunity cost of all Americans that allows them to start their own business. There are way more reforms needed too outside of that, which everyone already has to deal with in regards to starting a business.
So, imo, the complaint or point here shouldn't be that immigrants are better, or Americans are worse or there's only so much of the pie etc...it should be that we need reforms that makes it easier for everyone to start a business.