Big dent on frame: How did this damage happen?
It seems that this dent belongs in the bike.

Here is a photo of a similar bike. While image is of low quality, the dent is visible:



However, as pointed out by Lamar Latrell in comments, in your second photo the weld to the headtube has a dark spot in it. I cannot tell from the photo, but you or your bike mechanic should check if it is a damage in the weld seam, or just damaged paint.