You won't get banned for inting once. It take a few times, and even then, you probably won't be. Cause, here's the thing. No matter how many intentional deaths you have, I don't think the system will recognize it as inting if you have any kills, assists, CS, vision score, ect, because then it might just see it as a "bad game". I think in order to get banned for inting, literally everything has to be absolute 0 except for your deaths.
There's also, in my opinion, different kinds of inting. There's the just running it down mid kind of inting, but there's also stuff like this:
And probably a few more that I'm forgetting. But, you see, the running it down inter will likely have a far worse score than the other 2 inters, so the other 2 are less likely to get punished because they don't appear to be intentionally doing bad.
Also, was it the 4/22 Singed game or the 1/15 Anivia game? Both those games are pretty bad in terms of score and could be seen as inting depending on who you ask(I get that Singed's whole deal is "run it down and poison everyone along the way", but sweet Jesus dude).