I saw a thread on Reddit discussing this exact question. The user <PERSON> pointed out in a scene prior to when <PERSON> looked up the personnel list that occurred at 10:26 in episode 10, <PERSON> meets with <PERSON> and they agree to "compare notes" regarding their current job and <PERSON>.
The dialog they exchange is as following (emphasis mine.)
<PERSON>: I couldn't find much about <PERSON> in the public record...
<PERSON>: Me neither.
<PERSON>: ...So I tailed him to a naval logistics office in New Londres.
<PERSON>: He's a desk jockey.
<PERSON>: What's his rank?
<PERSON>: I think he's a sergeant.
<PERSON>: The security codes he's been supplying us with are high-level, typically restricted to commanding officers only.
<PERSON>: They're way above his pay grade.
After that conversation, at around 24:00 in episode 10, <PERSON> starts looking up other personnel that work in the same office as <PERSON> that may have that level of security clearance. The viewer can deduce this as the list of personnel says "logistics command" at the top.
The two people she looks into further are <PERSON>, Ring Probe Telemetry Analyst (presumably meaning The Ring) and <PERSON>, Protomolecule Working Group. 861
These people are shown to have security level 4 and 5 respectively, while <PERSON> is shown to be only at level 2 security clearance. The audience is therefore probably supposed to conclude that these people working with the Ring and the Protomolecule are the ones giving <PERSON> that level of clearance.
I'm personally not very familiar with military rankings, but the other piece of information that might supposed to be notable is that despite his level 4 security clearance, <PERSON> is listed as only a private, which to my understanding is a very low rank and definitely not a commanding officer, and <PERSON>, who has security clearance 5 is only a lieutenant, which by my understanding is only a low ranked officer. This is also in contrast to <PERSON> who has only security clearance level 2 despite being a sergeant, which should be a higher rank than private, and not that much lower than the rank of lieutenant even though <PERSON> said the security clearance <PERSON> was giving was "way above his pay grade."
At any rate, you can see in this scene <PERSON>'s reaction is to look very confused rather than shocked, so while the audience may be alarmed by words like the Ring or <PERSON>, <PERSON> is almost certainly supposed to be honing in on some other detail, which seems to me probably the descrepancy between their ranks and their security clearance level.
It then cuts to the next scene where she sees that <PERSON> is actually dead, and that's when she becomes alarmed enough that she tries to break up the sale.
As for "How did <PERSON> conclude the containers contain stealth tech?" the answer seems to probably be that she still didn't know what they were selling from her investigation into the logistics personnel until she went to actually break up the sale, and that she may have figured it out by recognizing them from her time working in the salvage yard. 865