Knowing the details now, the guy sounded like a bad salesman/tosser in his attitude.
I thought he might be expressing concern to you about the potential negative aspect of you going to 19 inch from 17 . May look good to some but don't think your soft stock spring and KYB shock will enjoy coping with them too much in term of performance , espscially with series of bumps thrown in. Getting a subpar tyre that you're not happy after speinding big on the rims is not ideal as your car performance and braking ultimately depends on the 4 small patch of tyres , especially in foul weather.( I did the same mistake too and paid for it)
Burg H6 SpecB has Bilstein B6 sport damper which can cope with his 1 up size change better . At the end of the day, you must be happy with your mod path and if you're happy , that's all that matter