Sunday
Recently updated the June security patch, unsure if it's something that coincided with that or it was prior as I use "Hey Google" (now Gemini) on my S23 usually.
However, just now I used "Hey Google" while the S25 was locked, to set an alarm and to my surprise it started playing the audio from the last Video I watched on my phone. Which I might add, wasn't the last thing I did on it either... (Outlook app)
Yesterday, I unlocked the S25, swiped away a Radio App I use frequently (after manually hitting the stop button too), locked the phone and accidentally triggered Gemini (it does it quite a lot) and a few seconds later it started playing the audio from the app I'd swiped away, somehow.
I've had the S25 for a while now (couple of months), but don't have much on it as I still haven't full switched over from my S23, and only recently updated it, so it's had a restart recently.
Even so, playing the audio from something I was recently watching, isn't something I want my phone doing while it's locked... Pretty concerning.
yesterday
Don't find it concerning at all, personally. See if you can tweak so that Gemini doesn't open on your lock screen