What is this silvery spot at the bottom of my wok after first use?

It looks very much like you've scraped off some of the non-stick coating.
Aside from the main peeled area there are other scratches that look like you were using metal utensils. You should be able to just feel the edges if that's the case, a very slight rise in the level between the 'silver' which looks to be aluminium & the 'dark' coating. It's very thin so may be hard to feel.

If indeed that's the case, it's time for a new wok.

I've blown up the photo to see a bit more clearly. The peeling could be from overheating, or just poor manufacturing. The scratches, however, are a separate issue, & look like heavy use of metal utensils, which 'old fashioned, regular teflon' just cannot take.

There are newer non-stick coatings which are much more scratch-, and indeed heat-resistant - but they tend to come at a price.

Late edit
As the subject of overheating teflon seems to always crop up in comments on this type of question, modern non-stick is quite often no longer described as 'teflon' or PTFE, but just as a rather secretive 'non-stick'.
My own wok is one of these - Masterclass - and has withstood all the heat I can throw at it for two years, without showing any sign of scratching, burning, evaporating or anything else detrimental to the surface. I treat it with little respect, though I only use wooden or plastic utensils for all my pans, & wash it in regular washing-up liquid (dish soap) with the same brush I use for everything else. The outside is scuffed & scratched, but the inside still looks as new.
And it only cost 30 quid [bucks/euros].

As @Tetsujin says the non-stick has come off. I've had experience with woks of this type and I've never had the non-stick coating last, it's simply not durable enough to stand up to real wok cooking. These are really only suited to medium high heat, not the screamingly hot temperatures of authentic wok cooking, so if you used this on a wok burner it's very possible you exposed it to too much heat. They really are more of a wok-shaped saute pan.

If you do plan to keep using this type of wok then keep the heat under control and use wooden utensils as metal utensils will scrape off the coating very quickly. If you want to do more authentic wok cooking you should invest in a real wok and wok stand, seasoning it using the standard method. If you want a non-stick wok that can take high temperatures you'll have to spend a bit of money. I have a Circulon one which has stood the test of time and temperature, it's not cheap but I's lasted 20 times longer than the cheap ones and it's still working.

You scratched off what appears to be the anti stick coating off the pot. Which is why you don't use them. The best woks are made of high quality stainless