Well there are several facts there. IMO it should have been left up to the jury to decide if and how they are related.
For instance.
GZ claimed he followed Trayvon because he was acting strange. That's a fact. NO, that was his words, not a fact.
Trayvon had THC in his system. Also a fact. YES
Dr Bao said he thinks pot might have affected Trayvon's behavior. Also a fact. NO, don't you remember what he said? (Read my edited post)
Pot has been known to cause paranoia. Also a fact. YES
The judge is preventing the jury from weighing these facts.