can a Dahlia revert to a different flower than it should be

Not clear whether you're saying you've had these more than one year and they've changed, or whether you've planted them this year and they're not what the packet said. Its impossible to tell from looking at the rhizomes what they are, by and large, so if they're new, they've been packaged incorrectly. If they've changed this year from ones you had last year, then its likely some kind of reversion has taken place.

Have you had Dahlias from last year?, you can divide the tuberous rooted plants up each year if lifted and stored in a frost free place, very old ones often change colour.