Look mate, you don't have to be suspicious- you had no drama. I have been flying across the Atlantic for 35 years, and control is top notch. Briefly, Gander Oceanic control west of 30W, and Shanwick Oceanic control east of 30W. Pilots navigate and report every 10 degrees of longitude. Height separation on each route is 1000'. Routes at the moment are 1 degree, or 60 miles, apart. Some pilots apply a track offset of 1 or miles right of track as Nav systems are so accurate that in the remote event of an error, you won't be bang on course against another aeroplane coming the other way. You were looking at another flight 1000' searated, and maybe 1 or 2 miles away. Do you not think if you saw the other flight, one or the other's pilots could also? And they appear to have been not worried by it? When you get an explanation here from people that do know, you can rely on it, especially as your knowledge base is zero on these matters- I know what you thought you may have seen, what actually happened was different. It is common for people in holding patterns when turning to think the aeroplane above or below is at exactly the same altitude- another scenario when people don't believe the explanations!