It's a scumbag thing to do, I know, but some things are too beautiful to be shared, and you have to discover them for yourself. Gravity Falls is one of those things. I know you'll forgive me in time. (╭╮)
I feel like he just had no clue how he was going to do the next arc and decided "Fuck it, I'm just gonna have to use some of my end-game material here."
I'm still upset about how it was handled. It was just thrown out as a casual conversation. "Hey, Eren. Hi. So listen, I'm the reason humanity may be going extinct soon, and I'm the reason thousands have died, including your mother. Come with us. Oh, he helped too, by the way." Ugh. The biggest mystery was just thrown out on some random panel.
I caught up last night as well. I think it's cool to see the titan again that ate Eren's mother, but.. it's not really all that relevant, frankly. It seems to be just another titan.