Reusing old woods pallets as flooring

It's prolly got a roll on coating that makes it slick like regular flooring

I know but at first glance it looked like melted Popsicle on the floor

It's stained, it's used on wood to give it a natural darker color.

Naturally, you're going to cherry pick the best pieces, Then they are nailed/screwed to the subfloor (sheathing/plywood laid down on the joists first) so there should not be any trouble.