How did you test your FTP in Zwift? A ramp test, or ramp test light, or climbing "The Grade"?
How much warmup before the test?
I wonder if more casual Zwift riders don't do competitions or do an FTP test, so they don't show up in the stats.
Your 142 pounds is 65 kg. 151/65= 2.3 watts per kilogram. That sounds good to me.