"That's grandpa"

I was sitting here at my desk tonight and my son, Noah, comes up to sit on my lap. He likes to sit with me when I work sometimes. I have some pictures under a clear mat on my desk. Right at the bottom where he could see, is a picture of my grandma and grandpa (picture above). The same grandpa who passed away at the end of this past October.

He pointed to this picture and said "that's grandpa".
I said, "yes it is, Noah".
He went on to say "grandpa is sick".
I said, "yes, grandpa was very sick".
He continued, "and grandma was with grandpa . . . grandpa's sick". (He was talking about my mom - we always were with her when we visted grandpa.)
"Yes, grandma was with grandpa a lot when he was 'sleeping', wasn't she?", I replied.
Noah responded, "yeah . . .".

He then went on talking about something else. He then came back to the picture.

He said, "who is that, mommy?", pointing to my grandma, who is with grandpa, in the picture. He never knew her.
I said, "that is grandma. Mommy's grandma."
"Oh", Noah said. "Grandpa likes to sleep", he continued.
I said, "yes, grandpa likes to sleep. Grandpa was really sick. He is sleeping now".
I went on, "grandpa loved you very much".
He said, "uh-huh".

And that was it.

Those words, those memories, are from 38-month old little boy. It makes me cry. I sit here in tears. I'm not sure if it's because my baby remembers grandpa like he does; dying. Or that soon he won't remember anything of him. Or that I just miss him. I think it's probably some of all.