If you can spell correctly, then you can also capitalize correctly. In fact, it's a whole lot easier to remember that a sentence begins with a capital letter than it is to spell every word correctly. It doesn't matter if your "rambling online about plastic models" or composing your Master's thesis–either you're doing it right or you're not.
Either way, it makes no real difference to me. I'm neither the grammar nor the spelling police. I was just pointing out that I found it odd that you would be criticizing someone else's mistakes when your own posts had mistakes in them!
I mean, first you publicly accused the kid of lying, basically... with no real proof, just a hunch on your part? That alone seemed strange to me. Then when you also decided to jump on him for his lack of spelling skills, well, I figured maybe I should point out the irony in that.
Like I said, I'm not taking sides or picking a fight. But if you're going to be critical of someone else for mistakes they make, you probably should be sure you're not making similar mistakes yourself.