Eyewitness? Certainly not. Josephus was born AFTER Jesus died.
What we do have in Josephus is mention of one or two biblical characters (including James), and also an early account of Christianity that is often used by less well informed apologists. This early account however was added to by later Christian scribes and copyists, however even when removing the interpolations you have a very interesting piece about early Christianity.
Taken from something I wrote elsewhere
About this time there lived Jesus, a wise man, if indeed one ought to call him a man. For he was one who performed surprising deeds and was a teacher of such people as accept the truth gladly. He won over many Jews and many of the Greeks. He was the Messiah. And when, upon the accusation of the principal men among us, Pilate had condemned him to a cross, those who had first come to love him did not cease. He appeared to them spending a third day restored to life, for the prophets of God had foretold these things and a thousand other marvels about him. And the tribe of the Christians, so called after him, has still to this day not disappeared."
- Jewish Antiquities, 18.3.3 63
Historically there have been times in which the whole thing was taken as truth by the early christians, but then during the enlightenment the whole passage was questioned.
That passage is wideley accepted today as authentic, but also having certain interpolations, possibly made by early Christian copyists.
The first line uses phrasology not common among early Christians, and therefore seems authentic, however the second part of the first sentence, 'if indeed one ought to call him a man', implies directly that Jesus is more than human, and is probably an interpolation.
The second sentence too appears authentic, but the third, the statement, 'He was the Messiah', also appears to be an interpolation. Elsewhere in Josephus, in reference to James, brother of Jesus, Jesus is noted as being called the Christ, and it appears unlikely that Josephus actually believed this.
The second section,('He appeared to them...' - '....marvels about him'), also seems to be an interpolation, and unlikely statement of belief in Jesus in the resurrection.
However, even with the interpolations removed, this passage DOES seem to indicate several things about Jesus - that he was a martyred religious leader, was considered a wise teacher, and acquired a lasting following despite being crucified at the hands of Pilate under pressure from the Jewish authorities.
BUT in 1972 an arabic manuscript was found, which may have NOT been interpolated, and the translation of which is thus:
at this time there was a wise man called Jesus and his conduct was good, and he was known to be virtuous. Many people among the jews and the other nations became his disciples. Pilate condemned him to be crucified and die. but those who had become his disciples did not abandone their discipleship. They reported that he had appeared to them 3 days after his crucifixion and that he was alive. Accordingly, he was perhaps the messiah, concerning whom the prophets have reported wonders. And the tribe of the christians, so named after him, has not dissappeared to this day.
this is PAul Maier's translation available in "Josephus, the essential works" pg. 269-270
I'm not too familiar with this manuscript, or this version of the translation. But I'm told it exists.