I don't see that it matters whether the TSO doing the search personally believes there's WEI in the bag. What's relevant is whether they are searching for WEI or not. In the case you cite, they are, because you believed (correctly, as it turned out) that it was there. It's like if I call a friend who's house I just left and ask him to look for my sunglasses. He may say "I'm sure I saw them in your hand when you walked out" and not believe they're there, but if he humors me and looks for them, he's nevertheless still looking for sunglasses.

In Fofana, the TSO testified she was not searching for WEI: in other words, not only didn't she believe it was there, she wasn't looking for it. That's the difference.

The interesting thing in Fofana, in my opinion, is that the way the decision was written, it seemed to hinge almost entirely on the testimony of the TSO. If she'd said "I hadn't decided that the bag didn't have WEI", would the search have been permissible? That would have been a much harder case because the relevant standard isn't clear.

I don't think whether the TSO followed the SOP or not is relevant in cases such as this (meaning the fact that the court didn't have access to it didn't matter) because the fact they were following the SOP doesn't matter if the effect was to exceed the boundary of an administrative search (i.e., some part of the SOP may be unconstitutional). I think it's an interesting question what the variant of the "reasonable person" standard would be here. Maybe something like "whether a reasonable person with knowlege of the security issues used to generate the SOP would think that WEI might be encountered doing the seach in question".