Starter Help

I was planning an making some sourdough pancakes so I used some of my sourdough starter that I was going to discard to make the batter ahead of time. I fed the starter this morning because the recipe calls for "fed" & "fairly thick" starter. I fed the starter with some Walmart brand all-purpose flour. I left the starter out while I went to my classes today (I left at 9am) and returned home about 5pm. What I saw I did not like. Little grey/black dots all over my sourdough and even up some of the sides where I had mixed in the flour this morning (see picture). When I took a spatula to the mixture I could see that the mold was only a very thin layer floating on top of the rest of the batter, but mold scares me. Especially when it is not green but grey or black. I think it is the flour from Walmart. Let me qualify that statement. The first time I used this AP flour after I purchased it, it ended up ruining my secondary batch of refrigerated starter. I feed both of my starters weekly and this particular starter when I pulled it from the fridge was inudated with mold everywhere, like some mad science experiment! So I was shocked and saddened. Shocked that mold would grow in my starter at such a rapid rate (I feed every 5 days). So my white flour starter I had to throw out but there was enough to salvage underneath the mold that I started a new batch. Now my whole wheat starter that I feed with only King Arthur brand whole wheat flour has never exhibited any problems with mold. I have had a white flour starter for some time now but trying to pinch pennies I regretfully bought the cheapest AP flour at Walmart and now I am regretting it. Am I right in thinking the Walmart flour caused this since using this flour twice in two seperate starters has resulted in an outright full fledge bloom of mold? I am considering throwing away this bag of Walmart flour and vow to never buy it again. I need to add that I made the pancake batter in a clean, (freshly sanitized from the dishwasher) stainless steel bowl. Trying to understand if that may have attributed to the rapid mold growth. So confused.