Most likely this is exactly as it appears. Lukaku didn't like being Dzeko's bitch at Inter & showed his immature, greedy & disloyal side. But there are a couple of wild "theories" that could also explain this turn of events:
1. Juve have Conte lined up to take over this summer. That would explain why Juve want Lukaku & why he is so keen to go there. However the cost of Allegri's contract makes this unlikely, though anything is possible.
2. Another theory is that Marotta & Lukaku are in sync & are calling Juve+Chelsea's bluff. Juventus did this to Inter last time with Lukaku as well, which resulted in Inter paying extra. Maybe this time Marotta knows that Juve are only dicking around (coz signing Lukaku goes against their wage reduction strategy) & Chelsea are using that. The less Inter have to pay to Chelsea, the less Lukaku has to reduce his wages, so he is onboard with this. And they are calling Juve's bluff. Once Juve back off, Inter will renegotiate with Chelsea for a reduced amount. One thing supporting this theory is that Lukaku/His Agents/Marotta haven't publicly said anything yet. But still, this theory sounds too far fetched.
Lets see what happens. If Lukaku ends up at Juve or Inter, or Conte is signed or not, we will know.