I suppose it is possible to fake metrics without lying...you just have to be very misleading. The "number of users" metric, for example, is not clearly defined. Does it mean total number of warm bodies who signed up? That's hard to fake. Is it the number of rows in your user table? That's easy. If people can register multiple accounts, then 1000 people could have 10,000 accounts and claim 10,000 unique "users".
It is also easy to get users by having a free tier. You could have 100,000 free users and 10 paid, and claim to have "100,000 customers". Or if your service is targeted at businesses, who then resell to their customers (an MLS service for example), then you might claim that your service is "used by 100,000 customers" even though you only sold to 100 businesses.
You also have to read the wording carefully. There is a dentist near my house that advertises "We specialize in Zoom teeth whitening, as featured on Extreme Makover". You might assume the dentist was featured on the TV show, when in fact it was only the Zoom product/technique that was featured.