He probably put his finger on the trigger out of habit, doubt he hit it. The Glock has a safety built into the trigger. The trigger is split, with a very "small finger" between the split. When you place your finger on the trigger the "small finger" is naturally depressed releasing the safety.
From the Glock website, http://www.glock.com/english/index_options.htm look under "connector". They offer 3 different trigger pulls, 4.5, 5.5 and 8.0 LBS. My G23 / 40 Cal has the 5.5 pound pull, if owners feel the 5.5 too light, then take it a gunsmith and have the connector replaced with the 8.0.
From the pix your sister shoots competition, the handgun is a 1911 or variant, cal could be 9mm, 38 super, 40 or 45. Comp guns have very light trigger pulls.
She told me that the trigger pull on her Glock is the lightest they make but she didn’t give me a number. The trigger pull on my .380 was an 8. Hers was probably about half that according to your numbers.
The Glock my husband had for a few days had the split trigger you were talking about. He bought it from the retired LEO that shot the TV because he wanted to try one and the LEO wanted rid of it. I didn’t shoot it but he said the trigger pull on it was lighter than any gun he had ever fired. I wanted to shoot it but he felt like it was dangerous. I guess I’ll never know. LOL He is not very adaptable to change and the Glock was too different from anything he was used to. My .380 had a decocker and he didn’t like it at all even though I felt that it made it safer. He didn’t have any trouble re-selling the Glock. I thought it was a beautiful gun but it was only here for two days.
When I carry the Glock, I use the little plastic Glock safety that sits behind the trigger, and prevents it from being pulled. Works great. If you need to present the gun, just clear the holster and pop out the plastic trigger guard with your trigger finger. Maybe adds .2 seconds to the draw.