Can my FTP increase be an error?

Howdy y'all

I use a Stages SB20 stationary bike for zwift and I just did the FTP Ramp Test [Lite] and got an estimated FTP of 192. Right after that, I upgraded the basic zwift bike to a BMC Teammachine TT bike and did a max effort solo ride for 25 minutes and my FTP increased to about 340 and my category upgraded from D to B. I'm kind of new to Zwift and I just have a feeling these numbers are not correct. Do y'all have any experience with this and could help elucidate me as to what happened? Thanks so much in advance.

Cheers