Can I use a wood polyurethane coating to cover tile/grout on a bar?

The guy at Lowe's said instead of a sealer he recommended a polyurethane coat to protect the tiles in case a glass is slammed down or something to prevent a tile getting cracked or chipped. It made sense so we went with that. The can he picked out for us says it's for wood though. The directions don't mention it being used for grout or tile anywhere. My question -is it still ok for us to use polyurethane? And if so did he just hand us the wrong kind of polyurethane on accident?