He made no reaction to it of any kind, it came from a fake, thus it is no data point at all.
Riker was deducing that Rice was fake, or at least coming to the conclusion that there was something very wrong with his friend. When Rice made the warp 3 comment, Riker’s response was focused on the Drake still possibly being operational. So he did have a reaction, it just wasn’t in response to Rice’s top speed comment. In short, there’s no evidence either way that Rice’s statement was true or false.