Does it seem like squirrels are getting braver around people these days? I notice animals changing their behavior based on what we do all the time. We put in all this work to set things up right, and then a wild animal just takes over the plan. Your picnic still avoided trash, but the squirrels got the meal instead, which is kinda funny. This happens with more than just food, like when life messes up any careful idea we have. It's a small reminder that we don't control as much as we think.
Back in Seattle, squirrels grabbing food is just part of outdoor eating. Those sandwiches going to them is still zero-waste in a way, since nothing got thrown out. It's like an unexpected animal picnic share.