ISS Fan Club

Hello.

Last saturday, 29 March, I've been spotting ISS in naked eye, as I usually do as weather permits.
To get my observation opportunities I following a link from Heavens-Above, created based on my location, in the north of in Portugal.
Here is the link to last saturday's spotting: http://www.heavens-above.com/PassDetails.asp?SatID=25544&lat=40.54305&lng=-8.05205&alt=317&loc=Naia&TZ=PWT&Date=39536.8096077849
Therefore, visible from aprox 19:23:02 to 19:28:44

Well, the sky was clearly fabulous, on that start of evening.
The stangest thing was that I saw a bright object, ca 1/10 the size of ISS, leading it by
(I can't be accurate in this one) aprox 5km, the whole visible trajectory...
At that time I got really excited, cause I thought it could be the ATV Jules Verne.
But going back to the Heavens-Above site, changing the "satellite" to ATV, we get: http://www.heavens-above.com/PassDetails.asp?lat=40.54305&lng=-8.05205&loc=Naia&alt=317&tz=PWT&satid=32686&date=39536.8154817014
Visible from 19:31:35 to 19:37:01

See the time lag? So the ATV is trailing by around 8 minutes, not leading...

Can someone explain what I saw then that evening? I am very curious.

Thanx