When photos from G-Dragon (with Seungri) were posted, a lot of Addicteds noticed that his pose alone showed two signs - he's wearing the ring and their sitting position were the same.
And when it finally aired.. BAM! Yes, it's like their guesting has similar story line.

They both talked about their mothers. 
(Bom's was about her deceased aunt though who was almost like her own mom for her)
They both cried/almost cried.

Their talents were soooo funny.

Their reactions were almost alike.

Both tried to laugh, but tears started to flow.

Their reaction when they agreed.

Their sitting positions.

Watch GD&Seungri on Strong Heart - Part 1 | Part 2
Watch Park sisters on Strong Heart - Part 1 | Part 2

Caps by: G-BOM Baidu
GIFs by: Twiddlebug + tumblr