couple of questions for someone familiar with torrents

[d3adf1sh 1]

1) so i don't do a lot of torrenting but sometimes i'll download music torrents which not many people do these days so i'll seed for a bit longer than usual.  but sometimes i'll notice after it's been up for a while i'll see a peer trying to connect to me using the same port number that i use, which is weird because i use an oddball number that was assigned by air.  thing is it's always from china and i could see if maybe a coincidence that someone could be using the same port as me if it only happened once, but i've seen it happen quite a few times and it's always from china.  

i guess my question is, is it someone trying to hack me or something? i figure that would probably be next to impossible being i'm already using vpn and firewall and what not. but if you were using your actual ip adress and they knew which port you had open is that something they could use to get in to your system?  really i know it's probably no big deal, just bugs me when i see it. 

2) i also see people sometimes that will be using both ipv4 and ipv6 address and showing up as two peers i guess to speed up their downloads, but to me that's cheating so i'll usually just ban one of the addresses and they can get one connection like everyone else.  my upload slots are limited so like i said seems like they're cheating.  kind of wonder how they get that to work, but really i'm fine with waiting 30 min or whatever it takes to get my free product without being a pushy a-hole.  reminds me of people that go through the 10 item express lane at the grocery store with 25 items.