The idea that Lag ba'omer is the date of Simeon bar Yohai's death comes from the Zohar, where it is said that on the last day of his life, he received his most important revelations. The Zohar doesn't go back any 1,800 years. Also, the same date, it has been found, was the hilulah, the celebration of a death, of someone else in Tsfat, and only later did the celebration turn to be the celebration of the death (and date of revelations) of Simeon bar Yohai.
Report: Palestinian, 18, killed in clashes with IDF in West Bank (Haaretz)
from the article: Leaving the ultra-Orthodox high and dry