I was told by one supporter that there is a case of comma splice in the following sentence:
When he was able to crack the Trident code, that was deemed by many as his major achievement in his cryptology career.
I've checked the definition of comma splice in the Wikipedia and read there that:
a comma splice or comma fault is the use of a comma to join two independent clauses
However, when I re-checked the sentence, I noticed that the first part of it (the one preceding the comma) is not an independent clause, but rather a dependent one because it starts with when.
Wikipedia gives a similar example of such dependent clause and lists it under the category "adverbial clause":
When he was in New York, he went to the Guggenheim Museum.
So, this is where I got confused. If the given sentence is consisted of a dependent clause and an independent clause, and a comma splice case is by definition a case of splicing two independent clauses, how can the given sentence then be a case of comma splice?