Both may be correct:
"Engineered" floors often have a fairly thin, yet substantial, amount of hardwood laminated over a base of cheaper wood. This section can be as much as 3/8" thick, and can be sanded (carefully!) several times before hitting the laminated section.
Apart from the methods suggested previously, you can wait for winter, when solid floorboards will shrink substantially, allowing you to get a knife through and pry them apart. "Engineered" floorboards don't shrink quite as much, and are typically 'lighter' colored on the tongue and groove section.
Finally, you might also be able to drill through the subfloor from underneath to look at the bottom of the boards, or, if you have a cutout for a floor-mounted electrical outlet, that can be used as well.
As an FYI: a floor can often be refinished without sanding; the technical term is 'screening'.