musical

landed the other day to see a big queue, 3 e-passport gates operating and the rest not functioning. I was having a bad day and used my phone to snap a 6 second video of the e-gates to post on twitter and have a bit of a moan (it does my nut in when they don't open more gates). i didn't see any 'no photography' signs (AFAIK they are only by the personnel-controlled booths but there certainly weren't any where I was standing in the queue). A guy approaches me, tells me 'no filming' and I apologise and say no worries but I didn't see any signs saying that, otherwise I wouldn't have done so. He said to me 'I'm not arguing with you, I'm telling you no photography'. Which annoyed me and instead of just going on my way I (perhaps stupidly) said 'can you show me where the signs are that say that? otherwise how am i supposed to know?'. He smiles, immediately tells me i'm a security risk (?) and asks where my passport is. Then (the annoying bit) without waiting for me to offer it to him he literally grabs it out of my hand, says to me 'now I'm going to delay you even more', marches me to another desk and tells a couple more staff that I was filming. They look a bit embarrassed (I get the impression they know that this guy is a bit over-eager), ask me to show them the footage and delete it in front of them, which I do. They didn't ask me to delete it from the 'deleted items' iPhone folder. Then they, oddly, fast-tracked me through immigration and wished me a nice day.
An hour later I post the footage on twitter briefly explaining the situation and receive an apology from LHR's account (they didn't say photography wasn't allowed).
Question I have is, was I in the wrong shooting video (you couldn't see any people, just a row of around ten non-functioning passport gates)? I think i probably was but can't help feeling the guy over-reacted somewhat.