It looks like the main source for this article came from ATTOM Data Solutions, which is owned by RealtyTrac - RealtyTrac, for those who don't know, consider themselves a "real estate information company" as well as marketplace for foreclosed and defaulted properties.
What stuck out to me most from the article was this section:
It's easy to overlook this quote, but this is worth watching closely, in my opinion, over the next year especially. I get the sense that any sort of bubble here would originate from a drastic increase in the foreclosure rate for investment property loans given all the capital that's flowing into this sector, especially as more articles like this one will only further push house flipping into the mainstream with people (even more so than it is already).
Like @Chris C. said, "The Big Short" was a way for us to understand that money was being loaned to people who shouldn't have qualified by banks who were being greedy. In this case, if banks get greedy to lend money to investors who aren't really qualified to flip homes, and they don't stay conservative in their underwriting, they will once again end up lending money to "newbies" as investors who make mistakes and could easily get under water in the event of a recession or correction in home prices. I'm not saying it would be as severe at what we experienced in 2009, but it would be enough that investors like the rest of us would feel it. But this is all just speculation on my part, obviously.