Seen the pics on my phone now. Clearly at least a few hundred people there. The 10,000 is I think the estimate of the organisers rather than the police. I think demo organisers always overstate numbers, and of course those who disagree with the sentiment always under estimate. Shame no one took a picture from a building to validate it better. Lots of demonstrations all over the place though. I seem to see a few industrially related demos every year on TF3 in France but they don't even make the national French news. Someone is deciding how big an issue needs to be for coverage. I think there were a lot more people making a nusiance of themselves in Glasgow on Saturday than there were in Rome for example, and the understandably local bias will influence editors choices on what makes the headlines.
Apparently there was a 15,000 strong pro-refugee march in London in March 19. I don't know if anyone saw it reported? I can't find a BBC story covering that, and it was bigger and much closer to home. There was a similar march in Glasgow on the same day but as far as I can tell that only made the "Scotland Politics" section.
My point is I don't think these are conspiratorial media plots. Just editors believing people are more interested in local news, and demonstrations needing to be huge to get coverage. Look at the anti-austerity march in London recently with 100K (?) which I don't think made the TV news, although I don't think that decision did editors any favours.