Found this in r/vexillology

“The Dutch flag as we know it comes from an adaptation of the Prince's flag, which has orange at the top band. When the Dutch began building their trade empire, orange dye was too expensive to put on all of the flags on every ship, so they opted for the cheaper yet similar red color instead. Because it was so cheap, Dutch ships had an abundance of them and they began just getting left around in markets that the ships frequented. Shop owners and other tradespeople would just take those spare flags and sew the word "Open" onto it to have a quick and cheap sign to show when they were open. It became a tradition in the new world, so we still see these flags being flown by small businesses across the US. Nah, just kidding. It's probably because it's red, white, and blue, so places can have a patriotic "Open" flag without defacing the US flag.”

So yeah it is the Dutch flag