If it was difficult to pull and still had a lot of fat that didn't render, then it needed more time. Checking temp with a second thermometer will do NOTHING to fix that. Poke it with a bamboo skewer or just use your thermometer as a poker and poke the meat. When it glides in with little resistance, it's done. Some times it won't get to that point till 210 or more.
I also find resting for a minimum of 2 hours works great for any large piece of pork.
And don't give up on picnic roasts because you undercooked one. They are wonderful eating. Many people prefer the flavor of picnics over butts, me included.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. Weber SJS. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)