I'm hardly surprised. Without looking up the chapter and verse, I would suspect that it would take a (very brief) inrush of at least 20A to trip a B6. On some circuits, I have umpteen (simultaneously switched) LED lamps running off one B6, and have never known it to trip on switch-on.I have three of those fittings in the link (two switched together & a third on its own switch) on a 6A MCB with other lighting and never had a tripping issue.
Kind Regards, John