Perhaps it was a second that slipped through by accident - an air bubble where it shouldn't be, I would have thought, would have been enough to get it put in the "second" category?
Whatever, it's marked as a first, and if you love it, don't worry about it, just enjoy it!
I did buy myself a Caithness weight recently (charity shop, Â£5) marked as a second - the whole pattern of colours and bubbles is completely squint inside it, but I rather like it like that. (no idea what it's called)
Shame I let Michael carry it for me after I found it, it now sports a big bruise it didn't have in the shop!