"The research is based on a survey of creators for thousands of Kickstarter projects between 2009 and May 2015." Article is using kickstarter data, which was questionable in the beginning but now as kickstarter has greyed out would be even more questionable. What about using actual VC-backed company data? If you look there, solo founders are not only the (extremely large) exception, but they also have lower valuations and success rates.
Founding a company is extremely difficult and there is a huge amount of stuff to take care of. If you cannot find someone(s) you can delegate a portion of that work to, you will suffer. It's a signal for investors because it's a huge buy-in to become a co-founder, and solo founders burn out all the time.
Using kickstarter to share advice on VC isn't just misleading, it's downright harmful.