What does the Tigp on the nib stand for? I thought all 1911 pens were 14k...

Titanium gold plating. They use the gold plated nibs on some of their pens.

So is it a titanium nib with gold plating?

No I don't think so.

I believe it is a steel nib plated with titanium and gold. Apparently this plating is more durable than plain gold.

Most 1911 pens do come with 14k gold nibs when sold internationally, but I believe there are various models in the Japan market that come with TIGP nibs (or someone may have swapped the nib).

No, it is stainless steel. I'm guessing they use titanium during the process of gold plating.

So does it write better, worse or just as well as a regular 14k sailor nib?

I don't have firsthand experience with TIGP Sailor nib, but I would expect it to be as good as their gold ones. Below is Sailor Young Profit that comes with TIGP nibs for less than $60. The nib offering includes Music and Zoom. I might need to get one

http://www.sailor.co.jp/BUNGU/young-profit/index.html