No, the explosion of TWA Flight 800 was not cause by terrorist. The explosion was related more to maintenance issue and the fact that parts on a plane, have been know to break down. The issue with why people feel it was a terrorist act is that the information was never fully available and clear cut enough for those with conspiracy theories. There is no proof pointing to a terrorist attack, and no group ever claimed it, which they tend to do after an attack.
Investigators somewhat disagreed about the conclusiveness of the evidence of the TWA Flight 800. Initially, the consensus was that there were some mechanical issues with the plane that caused it to explode. Upon further investigation, the pieces of the plane showed signs that perhaps it had been hit by some sort of explosive or even that one had been planted on the plane.
Yes, the explosion on TWA Flight 800 could have been caused by terrorists, because the government never really said what the cause was. There were numerous witnesses that said they say a missile traveling towards the plane. Those witnesses were never followed up on and the witnesses were told to be quiet.
The explosion on TWA Flight 800 was not caused by terrorists. If it had been, this would have been plastered all over the news in this modern time of fear and war mongering. There also would have been some sort of intelligence on these so called terrorists, and there wasn't.
Initial beliefs regarding TWA Flight 800 led to a 16 month investigation carried out by the FBI, but that investigation led to no evidence regarding the possibility that it was somehow linked to terrorism. The explosion was cause by a fuel tank explosion caused by electrical sparks. Given the investigation and determination I do not believe there is any reason to suspect terrorism as the cause.