Hi,
Just because 2 or 3 people say there was a fire earlier based on observation doesn't mean they were seeing the same evidence. when examined in detail they are often not sure what they saw and precisely when, but vaguely remember their conclusions.
You right ...
The important part of a witness report is his first (hot) report .. not influenced by other news or events.
It's common to have from a same witness a different report after sometime .. cause he know others things linked to the event (by the press .. investigators .. police etc ..)
He is influenced by all this and can begin to have doubts and his view can change for many reasons (even a feeling of culpability)
It's a well know phenomena.
So it's the first report (immediately after the event) who is the more credible.