It's not a "trace", the artist simply colored it in his own style. He even linked to the original artist on the pixiv page.

Well, it's still a "trace" by any definition

However, the purpose of a deletion for "tracing" is for preventing plagiarism, but it's hardly plagiarism when the artist acknowledges and credits the source, while linking it in his own work.

Wallachia said:
Well, it's still a "trace" by any definition

"Trace" implies that one copied the lineart. It's not tracing when a schoolkid fills in a coloring book; this is the equivalent of such, just on a higher level.