Confusingly low BAC reading?

Hey everyone, I figured this might be a decent place to ask, but any idea why my BAC remained very low despite a night of drinking?

To elaborate, my friend purchased a reputable breathalyzer off the internet and we checked our BAC throughout the night for fun (not so we could drive, we all spent the night). A rough estimate of the alcohol we consumed was (per person) 3-4 beers, 2 oz of whiskey, 2 oz of rum, 2oz of tequila. If I had to guess I’d say this was spread out over around 4 hours. Consistently, my friends were in the 0.14-0.17 range.

I blew multiple times throughout the night. We always waited 20 minutes after eating/drinking. The highest I blew was 0.049, and the lowest I blew was 0.041. I felt substantially drunk, so I couldn’t believe I was theoretically below the legal limit. I thought something was wrong, but everyone else seemed to get accurate readings.

I’m about 195 pounds and moderately muscled. But I didn’t think this would have such a dramatic impact on my BAC, especially when I felt drunk!

Any idea why this might have been?