Ooh hang on. The filter as in inside where the sponge is was chock full of 'em or was it the inlet grid where the water is drawn in? Was it that bit that was jammed full? Are they fixed with jelly of kind of loose just rested on the leaves?
If they are goldfish eggs and they've been fertilised you will see a black dot in the middle after a day or so. Seen any courting behaviour - chasing, bum-nudging etc? Any of the fish with white spots on heir gill covers or front fins?
Got anything else in there that might lay eggs? Not sure what goldfish eggs would be doing in filter unless laid very near intake?
WCMMs are cool. They are the hardiest coldwater fish I have experienced so far meaning I have had absolutely no problem with them at all. They are really very pretty aren't they? Have you seen them fan all their fins out? Awesome!
I keep WCMMs with a Moor with no problem, though he is still a tiddler. I had no problem with larger ones either - they didn't seem to be interested in them, but do make sure you do a head count each day!