Petroleum implies long-chain hydrocarbons, the so-called “fossil fuel”. Generally, they require high temps/pressures to form. Methane on the other hand can form (and does) under lower temps.
This is a distinction without any significant difference; long or short chain, they are all hydrocarbons.
It’s only been in my lifetime that there has been any real concession by some that ANY hydrocarbon, even methane, can have other than a biologic origin.
It might be that nowhere on Titan is there sufficient temperature and pressure for the long chains to form. But there is on Earth, fortunately.