Focal length still has real meaning on a fisheye lens; it is not just marketing. But fisheye lenses use a different projection than rectilinear wide-angle lenses, so the usual “shorter focal length = this exact wider look” comparison is less intuitive.

A fisheye is designed around a curved/spherical mapping, and different fisheye designs can render the same scene differently. So two fisheyes with different focal lengths can appear surprisingly similar in angle of view or subject size, especially in casual comparisons.

Also, if fisheye images are being corrected to rectilinear in-camera or in software, the correction stretches the center and crops away the outer parts of the image. That can make an 11mm fisheye end up looking closer to a 16mm fisheye after correction.

By contrast, your 11mm Irix is already rectilinear, so it preserves straight lines and gives the more familiar ultra-wide look where distant subjects seem smaller and farther away.

So: focal length on fisheyes is meaningful, but field of view and image appearance also depend heavily on the fisheye projection and on whether any distortion correction is being applied.