I think the major red flag for me is the laxity in basic information security. I have worked in places that doesn’t do any defence or intelligence related work, and it was basically impossible to copy anything from the main secure server without IT security knowing about it.
I am hopeful that this means the data the guy was able to copy and steal wasn’t actually truly damaging. Because it would have been truly criminally incompetent to not have such basic data security measures in place for truly sensitive national security data, in which case many more heads would have rolled.
It also kinda makes sense that he only got such a paltry sum for his efforts, and also why the foreign intelligence agency basically ghosted him after the first transition. Even if he sold them everything he had, or they hacked his device and stole everything he took with him to the meet, if he had truly valuable stuff, they would not have ghosted him, and would at a minimum have kept in touch in case he managed to score anything else or had more stashed away offline back at home.
My take is that the guy did the classic marketing gimmick of making it look like he had juicy prizes to offer when he only had some basic stuff, and the foreign intelligence agency he contacted realised he was a time wasting conman after paying the fee to see what he had to offer.
He is being executed because of the way he so proactively went out of his way to betray his country, repeatedly. He wasn’t honeytrapped or approached and had a moment of weakness, he willingly and proactively went to seek out hostile foreign agents to sell out to. The stuff he sold probably is classified, but it shouldn’t be anything too critical. This was more about setting an example, which is why it’s so well publicised.