Yes it is correct, like most countries Thailand law is that a foreigner should carry at least a copy of their passport showing the details page and your latest entry visa stamp and the white departure card that is placed in your passport when you enter Thailand it can be for your own safety also I always advise having a copy of your passport because if the eventuality arose were you lost your original passport it will save you a lot of heartache at your embassy when applying for a new passport, if you call in at one of my offices for a small fee we can produce a credit card sized laminated copy of your passport which you can carry with you at all times with ease.