The search bar actually reads chicken not chicks so that could be why adult birds are shown.
And all of those are brahmas, just in various colors. So if you specifically wanted light brahmas, you could just search 'light brahma chicks' and then you get this:
All of those are light brahma chicks and adults. So, a little research can easily confirm if the chicks in the bin are actually what they are labeled to be. If you don't care what you end up with then it's not really necessary but if you want a specific breed then it's best to do research before purchasing, as you would do for all major purchases.
Would it be better to be able to trust that what's in the bin is indeed what they say it is? Yes, but since that's not the case, better to do your research before buying if you want something specific.