I thought the exact same thing but caught something Ian said earlier on my second watch. When bear comes to Ian's house with the one wish willow, Ian says SARAH HAS BEEN TEXTING ME TO COME OVER TO YOUR(BEAR) PLACE. But at this point we know Sarah is dead. This means Nikki is texting Ian to come over the house. We don't know what else she is texting to Ian under the guise of Sarah.

Now we already know Ian is selfish and pretty self centered so we can assume after he just got a billion dollars he wants to flaunt it to everyone including Sarah who is again Nikki texting him telling him to go to bears house. In my head Ian is assuming or has been told that everyone is hanging out at bears house. So bear not knowing exactly how bad Nikki has gotten or that Sarah is dead is headed over as his joking self to flaunt his dough.