It depends...
If a pilot or an engineer said something about what they saw in regard to an aircraft accident then you would give that a lot more credence than what your average citizen said, wouldn't you? Of course eyewitness testimony is always taken to be intrinsically unreliable but some eyewitnesses are more reliable than others.
An airport fireman has to be pretty credible when it comes to fire: sparks, smoke, flames and that sort of stuff are his area of expertise; while it isn't 100% absolutely established beyond any doubt it must be something that demands consideration, these reports about just where it was seen that this aircraft was showing the first signs of serious trouble.