TKD History Sources
"Taekwondo is a martial art that in "todays" form of self defense has evolved by combining many different styles of martial arts that existed in Korea over the last 2,000 years and some martial arts styles from countries that surround Korea"
Taekwondo History
This article says that it was created from many different styles of martial arts that existed in Korea over the 2000 years. The different martial arts styles existed in Korea not Taekwondo.
"The first Taekwondo school (Kwan) was started in Yong Chun, Seoul, Korea in 1945" This seems to be very late for something that has existed for 2000 years.
TKD History Source
History
They constantly refer to Taekkyon through their site. Then they try to make it seem that Taekkyon is the same as Taekwondo but they are different.
"The martial art Taekkyon (Taekwondo) had been secretly handed down only by the masters of the art until the liberation of the country in 1945."
This is the history of Taekkyon
Here's another source:
"During Korea’s Yi period (900-1050), the Chinese introduced two more martial arts to Korea:
subak, eventually renamed
taekyon; and
kwonbeop, which became the standard art for Korean warriors.
Taekwondo arose in the 1950s when several Korean martial artists combined Japanese karate with taekyon."
Korean Martial Arts History - Black Belt
The sources that I listed are why I would question a 2000 year old lineage. The other thing is that martial arts develop over time and never stay the same as the original root. For a martial arts fighting system to be 2000 years old would be really rare. Those who master a martial arts styles are always seeking to make their style better and in the process the style is changed and often times this changes results in a new name and a new fighting system. That has roots in an older fighting system.