Earlier, when Tolesli got up to pee, he found the object, recognized the word 'aliens', and slipped it into his pocket. Now, back with the expedition, he says he wants to stretch his legs and goes jogging in a loop around Orocide, and takes another look at it.
...Yeah no, he has no idea what it says. He did some thinking on the turbowing and that's okay. If the extra PDA is a gift for Lei, ignoring it hurts Lei. If it's something bad, ignoring it while carrying it with him hopefully hurts Lei at least a bit, even if it's not the maximally gullible thing he could do with it.
His problem now is that he has to talk to the emperor. The emperor might support the FD, but has not given any direct sign of that to Tolesli. If he reports the alien object, or even just fails to conceal that something interesting happened and thus makes the emperor suspicious, the emperor will remember the event. Tolesli doesn't how Lei emperors audit each other and what limitations there might be on the spy emperor's ability to evade detection. So, Tolesli has to act as if the emperor is genuinely Lei.
Elves are not as perfect at reading people as they pretend to be - observe that Tolesli got hired at the imperial shrine - but they're not bad at it. Tolesli's strategy so far has been to be boring, which works fine when he is busy gardening or thinking about gardening, and rarely interacts with elves, and will not work at all now.
He's heard that pretending distress can cover up the tells of a secret, but he'd have to lie about something distressing, and he is not smart enough to keep a complicated story straight while also mixing it up a realistic amount. He was, in fact, specifically warned against this during his single visit to FD for training.
He could leave. He could keep running, destroy the object once he's far enough away that no one will see the fire, steal some food in Kef, and go to... go to Nitalhel, not through the Argo aqueduct, but by turning felward and staying in the stormlands until he gets to the dark end of the Sota-Nitalhel border. That way, if he gets caught, it might damage relations between Lei and the Allheart Alliance.
Another option is to be too sick to talk. When he was trained in FD, a liefling gave him a way to arrange that: if he bites the tip of his tongue while clenching his butt, a nodule in his kidney will dissolve and release an infectious plant - a 'microbe' as Hestlierre was saying the aliens call them... And Tolesli is worried that the liefling was lying and actually it would kill him.
Oh, Hestlierre, there's a thought. Could he talk with Hestlierre on the grounds that he's feeling bad and is worried about an alien disease that spreads to catfolk? If the object is a gift, FD will get it, but Tolesli will definitely get executed and replaced with a loyal competent representative.
Tolesli's replacement is a problem with all his options where he doesn't stay a Lei representative.