After living here for 6 years, one understands the difference between a couple of degrees over 100 degrees things turn intolerable for humans. So comparing 104 to above that and often 115 to over 120, then 104 seems like a piece of cake, so to speak. 90's are still quite warm but don't feel really hot any more. So your brother-in- law speaks the truth.
Dick
heppnerguy