There are "sub maximal" Vo2Max tests. I don't know the protocol but they run you up so far then calculate the Vo2max from there. It's probably less accurate than a maximal test. I have seen it used at health clubs.
But since vo2max is pretty much useless as a training number, the accuracy of the vo2max number isn't important. I like how they give a number accurate to two decimal places when it's a guess based on a table. I agree that 28 sounds low.

What time was that power number for? Power by itself is useless, you also need the time. I.e. power for 5 seconds, 5 minutes, 60 minutes. You can maintain a lot more power for 5 seconds than for an hour because you can use anaerobic energy sources. An FTP (60 minute) power of 252 would be about right for a recreational rider your size. There's ways of estimating FTP without doing a 60 minute time trial.