Actually, I think you are both right.
My personal opinion is that he deliberately targeted Pulse because of his hatred for gay people -- which one could reasonably argue is NOT out of step with Islam generally (being gay is a crime in 40 out of 53 majority-Muslim countries, often with death as the penalty). And hatred of gays is very much a hallmark of radical Islamic groups. But I think CPanther95 is correct that knowing that doesn't really help us avoid further attacks. The way you prevent attacks is to identify terrorists before they strike, not by focusing on one particular target group.
As far as the false narrative, I think there are two groups of people focusing on the shooter's possible sexual interests.
There are many people who simply can't believe there are bad people out there, and that any time someone commits some horrific crime like this they must be crazy. For them, there must be something badly wrong with the guy's head...so maybe it's conflicted sexual feelings. Or indigestion...or whatever -- anything but bad. These folks may not have any particular political motive for bringing up that explanation -- they just can't believe someone could be this cruel and bloodthirsty. Unfortunately, they are mistaken.
The other group clearly has a political agenda: wanting to deny that there is any such thing as "radical Islam" or a "radical Islamic terrorist" and deflect the attention to another (any other) possible motivation. Those folks aren't delusional; they just have an agenda.