The stainless cooktop might be 400 series stainless (for high polish
look) rather than 300 series (more often a brushed finish)

400 stainless is normally magnetic, 300 stainless typically not
magnetic (but can be magnetic depending on alloy & cold working)

400 stainless does have the corrosion resistance of 300 series

Contact the dealer & the mfr for more information.

cheers
Bob