That shows how dangerous dead or damaged tries in a city can be, that tree could have fallen apart anytime
No, it will make good tinder, means it's dry. You can't burn wood until the moisture and sap ages out of it.
It'll catch easily, but I suspect most of the fuel value has been lost and it'll burn up very quickly. Rotten wood is light because it's lost lignin.
Like chopping a tree in a videogame