Can be either.

Crisp sandwich: https://en.m.wikipedia.org/wiki/Crisp_sandwich

Chip butty: https://en.m.wikipedia.org/wiki/Chip_butty

I think 'potato chips' is always American crisps, nobody specifies 'potato' for British chips?

Also fwiw, amusingly, your attempt to internationally disambiguate the terms fell down because Walkers is Lays everywhere except the UK!

Pretty sure that was crisps. Though a chip butty is also alright on occasion.