Yep Butyl
I think they use butyl tape, and not the liquid "caulk" type, but either should work to seal.
Was there not a frame around it holding it in place?
If it's no frame sort of thing I'd have to see it to make a better guess, but I would bet it's more of an adhesive of some kind. butyl as far as I've worked with seems like more like a sealant. In that case, I'd call them. I doubt if eternabond double stick would be meant for structural holding like that.
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