The quote actually asks folks coming to the informal sessions "but please don't bring anything really loud that other people may find irritating", the bagpipes (presumably highland warpipes) are just an example (maybe even a humorous one?)

In some contexts I enjoy the really noisy pipes, but not in most informal sessions; I need a bit of space, or maybe those pipes do.

Some pipes, such as the Northumbrian small pipes, I would welcome in any session that wasn't devoted to some single, other, music.

So, "Bagpipes: irritating?" No.

But, "Very loud instruments at any session:iritating? Hell, yes!