Lets us look at this passage:
51 And behold, the curtain of the temple was torn in two, from top to bottom; and the earth shook, and the rocks were split; 52 the tombs also were opened, and many bodies of the saints who had fallen asleep were raised, 53 and coming out of the tombs after his resurrection they went into the holy city and appeared to many. 54 When the centurion and those who were with him, keeping watch over Jesus, saw the earthquake and what took place, they were filled with awe, and said, “Truly this was the Son of God!”
Matthew was not there, he is re-telling what he was told and it seems by what was written, he was told this by those that saw this: people that were there, saw the curtain tear, tombs being opened and saw the bodies of those ressurected, inculding roman soldiers.
Mark mentiones only the Curtain being torn and Luke and John mention neither.
I don't think that there was a resurrection of the saints, because the only one to be resurrected was Jesus and no one else.
This seems to be a case of Matthew passing on what he was told.
DO I believe it?
No, I think this was a case of Matthew just passing on what he was told and letting the reader be judge.