OP is correct. When people don't understand something, they blame anything but themselves. And in this case, their decision of ISP is an extension of "themselves".

If you're being hit when you are clearly outside the AoE before the cast timer finishes, then that is most definitely your ISP. Unfortunately, many times you can't really do much to improve your ISP's connections because the routing is mostly on their end. For those with issues like this, I highly suggest getting a tunneling service to force a more direct route. They are fairly cheap at only a few dollars a month.

My Australian friend was having this issue, because as we know Australia is infamous for horridly bad ISPs and internet connections in general. He got the tunneling service and now avoids AoEs no problem. All he needed to do was improve his connection.