Variance? Grandpa just died

[PITTM]

My little sister just called me at work and said that my grandpa died. My immediate reaction was "grandpa who?".

Backstory:

Within 3 months of my birth, both of my Grandfathers had died. Both grandmothers live in Chicago, where I lived until I was 3, when we moved to california. When I was like 8 my grandma remarried. The guy was super nice and I still have this set of proof coins he gave me. About 4 years ago my grandma had a stroke and has been in a nursing home ever since. After the stroke, my grandma didn't recognize her new husband anymore and this kinda caused him to stop coming to visit her. The combination of being incapacitated/having no memory/far away made it so that I never really went to see my grandma(my mom would go once in awhile by herself) and never saw my grandfather.

So after my sister tells me our grandpa died I finally figure out what she means. She is kinda crying and stuff and I am super indifferent because I barely knew our grandpa at all, like i might have met him 3 times ever? All of this made my sister even more upset since she seemed like she thought I should have been sad. Am I blowing it here or what?