Can gelatin change color of butterfly pea tea?
From the Gelatin Manufacturer's Institute of America &quot;Gelatin Handbook&quot;: https://nitta-gelatin.com/wp-content/uploads/2018/02/GMIA_Gelatin-Handbook.pdf

Gelatin in solution is amphoteric, capable of acting either as an acid or as a base. In acidic solutions gelatin is positively charged and migrates as a cation in an electric field.  In alkaline solutions gelatin is negatively charged and migrates as an anion.  The pH of the intermediate point, where the net charge is zero and no movement occurs, is known as the Isoelectric Point (IEP) (28).  Type A gelatin has a broad isoelectric range between pH 7 and 9. Type B has a narrower isoelectric range between pH 4.7 and 5.4 (29-32)

Emphasis mine.
So it does not seem impossible that your various brands of gelatin were produced by different processes and that one would be more acidic than the other. If you had a Type A gelatin and your friend a low-pH Type B, that would explain what you were seeing.
I do not think your method of heating had any effect.