>>228650
One other part that I'm probably just overthinking.
Page 33, second panel
Yotsuba is counting: 一つ、二つ、三つ... 十二くつ
I'm guessing this is just her not having a firm grasp on how counting works, because I can't for the life of me figure out why there's a く in there (or a つ for that matter, considering you only attach that to numbers 1-9).
>>228660
Jumbo drives the truck a few times early on, but then later we only ever see him driving a regular car (like when they went to the farm).
The only two possibilities I can think of here are
1) Grandma is confused and thinks the truck belongs to Koiwai, and he's explaining that it's Jumbo's.
2) Koiwai actually did used to own the truck, and is explaining that he gave it to Jumbo.