I shot with the Holga quite extensively over 10 years ago. I must say it's strange to say that the “Holga look” inspired the creators of Instagram—because the result looks nothing like it.
Instagram did not attempt to create faux light leaks or to emulate the imperfections of the plastic lens (which is what I associate with the Holga look). If anything, some of the Instagram filters come closer to a well exposed instant film.
I think this has more to do with the fact that cell-phone cameras got much better.
2010-era phone cameras were pretty crappy.
My own Holga never had light leaks, and most of the effects I got out of it were done via double-exposure or cross-processing the film (a very common Instagram look).
Instagram did not attempt to create faux light leaks or to emulate the imperfections of the plastic lens (which is what I associate with the Holga look). If anything, some of the Instagram filters come closer to a well exposed instant film.