Good name, Thud!
In the past Thuds were used as attack bombers and also as Wild Weasels. F-4s were used and later F-16s. The IAF raid had F-16s and F-15s which makes me suspect that the raid was much simpler and much more crafty than all the other speculations here.
The attack didn't come from the south, it probably came from the east. This would mean that the IAF overflew
Jordan with tacit permission, entered Western Iraqi air space with US tacit permission and began a east to west run on Dayr as Zawr. Wild Weasels ahead of the F-15s took out the air defense in the area leaving the targets undefended and led the strike force across Syria all the way to the Med. Check the map and ranges. This is possible with tanks (reports that tanks were jettisoned over Syria) and a high speed run would catch the western based Syrian air defense units by surprise.
Doubt that the IAF would compromise their jamming technology when a beam rider could do the trick.
The vaunted Syrian air defense system is only as good as the people running them. While the IAF run to the sea would take some time, reports would have gone out from the target area and the Syrians would think hard about switching to High PRF.