Season 1 has a connection with Season 3/4

I have figured out that some episodes from Season 1 have connections with Season 3/4 episodes. In Evicted!, Marceline says she hoola-hooped in the Fire Kingdom, and in Incendium, Jake goes to the Fire Kingdom. Also in Evicted, at the end, the Worm King turns up, and King Worm is a Season 4 episode. It's actually pretty weird. What do you guys think about how they're connected?