AWS charges me $1 or $2 every month, and I log into my account and click through every page and can't find a single active service or any clue on what it's for. It's marked "EC2 - Other", whatever the f that means
People forget to clean them up after shutting down the instance (probably kept in case you want to keep your IP)
Considering the whole IPv4 extinction that's coming down and all.
Not saying it can't happen, but I've never seen an 'Other' listed on the bill details screen. As I said above, it's detailed to a fault.
I haven't used Lightsail, so I'm not sure if those snapshots end up in the general ec2 console. But, if you already checked the LS console and didn't see anything, then they must be in the ec2 console.