WLAN data (Apple TV) being counted as ISP network data?

Hi, Here's an interesting one, just wondering if anyone has come across an issue like this before.

Is it at all possible that my WLAN traffic (local playback of content from my Mac HDD via Apply TV) could be counted as ISP data usage? Read on...

I've got a new 4G wireless USB modem (Huawei E3276 - iinet through Optus Australia, just commenced the plan about a month ago) connected to a Dovado TINY router. The Dovado is creating a local wireless network that other computers and Apple TV are connected to.

I'm on a very small data plan (only 20GB) a month so I've been very cautious about usage. I work from home and have been using 4G for work only.

Average daily usage of my 4G plan's wireless data has been about 400-500MB except for a couple of spikes of around 1.5-2GB on 3 days, a Friday, then Friday and Saturday the week after. These spikes are what I'm concerned about. The WLAN is password protected, I've got no reason to believe there is any security issue (Ie. someone else connecting to WLAN and using the data).

I can't think of any reason why the usage is so much higher on these days except for the fact that I was watching quite a bit of Apple TV on those evenings (like I said, this is local traffic, NOT content downloaded from iTunes store). Could this setup (Apple TV - WLAN - router - 4G USB wireless modem) be reporting local data usage as 4G ISP network data usage?

1. Is this at all possible, or has anyone heard of this before?
2. Can anyone suggest some tools to run a test to confirm one way of or the other (without burning through large amounts of data allowance).

Strange one I know, but any help would be appreciated, thanks in advance for any help you can give.

EDIT:

I should mention I've raised this issue with the ISP, but they haven't been very helpful.

Why not?

Also, do you have any ideas of a test to run to prove/disprove? It's just too much of a coincidence to let it go with a simple 'no'.

Sure, well that's what I would have thought.

So what's the test routine to run in order to prove this one way or the other? I've played around with a few things like Activity Monitor and Little Snitch, but I can't get my head around the procedure to actually check this.

Can someone explain the different processes going on here and what to look out for? Maybe this isn't the right forum for my questions...? Although if you guys are confident to say no it's not possible, I guess you understand all this well enough to explain why not, and how to test?