Grandpa sweeping chimneys in Ireland is a nice detail but it probably has nothing to do with the tip. Dude was in Boise, maybe he just had a good day or felt generous or was showing off. People hand out big tips for all kinds of reasons and half the time it's about them feeling good, not about some sweet backstory. The chimney thing is just a fun thing he said to make small talk. If you want the truth, the tip was about you doing your job right in that moment, not about some old man in Ireland decades ago.