I think Djilas' point is that England's largest island is Britain. Of course, England being only a part of Britain makes this statement somewhat problematic, but the quoted source does mention Britain and its contextual "mainland" status as the reason for its absence from the list.
The three legs symbol is a common variant of the triskelion, an old three-pronged spiral design found especially in Celtic areas. No idea why Sicily (and the Naples coat of arms as well BTW) feature it though.
The entire notion of a border between Europe and Asia is cultural much more than it is geographical. For that reason, unless there's a very clear geographical feature that has to take priority, it makes sense to follow country borders. Past the Dardanelles, there's basically no border-like geographical feature at all. Placing Cyprus in geographical Asia is ultimately arbitrary but at least it doesn't defy logic, splitting Greece between the two continents is just pretty absurd.
Remarkably, the flag of Sicily also features three legs in the same arrangement.
largest cities