I immediately called it a balk in the chat last night, still think it was a missed call, and your photos prove it even more for me.
Having said that, and I'm not excusing the 3B ump for missing it please don't get me wrong here, but I bet I can count on my hand the number of legit pick off attempts at 3B I've seen in the many thousands of college, high school and MLB games over the last 50+ years. I'm talking legit attempts. Not the step off and fake over to 3B by the pitcher type of stuff. In other words, and again no excuses for missing it, but I bet it completely caught the 3B ump off guard. He was likely as surprised as everyone in the stadium or us watching online.
I get the frustration by fans about our base running miscues so far and it is warranted. Having said that, I bet we don't get picked off at 3B again this season...and, those who have made mistakes will likely learn from them and get them out of their system this first week of the season while we are still winning big against inferior opposition.