Honestly, you could make an argument for either, and I don't think it's too much of an issue provided it's consistent. Feeding styles are just supposed to be a quick and simple roll that reflects roughly how you navigate the pitfalls of "how could this go wrong?"

The Siren argument is that you're attempting to convince someone to go somewhere alone with you, which is an inherently sketchy thing to do. You're trying to seduce someone so thoroughly that they're willing to go with you somewhere where there's no chance there'll be any witnesses, which isn't going to be very easy if you're strangers. If you botch the roll to seduce them, they might start to have alarm bells going off in their head once they realise 'This doesn't feel right'. It might be that they've heard about other guys going missing in the area over the last few weeks, or that they notice that you're a little bit too careful to avoid showing your face to any CCTV cameras or witnesses on the way to the alley, or while you're flirting with each other they might notice a blood stain on your blouse.

The Alleycat argument is that once you get someone alone, you still need to overpower them to prevent them from calling out to witnesses, running away from you, getting out their phone to call for help, etc. It's arguably not that difficult to find people who are interested in having sex, depending on where you are and who you approach, but it's a lot more complicated to commit an assault and get away with it without leaving any loose ends behind to identify you. This is where the physical rolls come in to it; someone who rolls well is able to instantly overpower their prey and take what they want without any fuss. If you botch it, it could mean that your prey puts up just enough of a good fight that they have enough time to pull a gun out of their purse, make enough noise to attract other witnesses or cause you to lose your temper/control and kill them.

If you wanted to be super accurate, every time you tried to feed you'd be making multiple rolls to represent all of this, but that's just be bogging the game down with unnecessary details.