I don't wish to make excuses for the loathful Reform, but it isn't a big deal.
It was a Westminster Hall session to discuss a petition that had reached the 100,000 signature threshold. It was not a House of Commons session. All Westminster Hall sessions result in a motion "That this House has considered...." and that's it. There is no voting. A rule to note is that "the quorum for a Westminster Hall sitting is three, including the Chair" - yes - they are that important.
Looking at the footage and Hansard, the number of attendees was around 25, and I can't be bothered to identfy everyone, but I counted 13 Labour, 5 Lib Dems, and one each from Con, G, PC, DUP and SNP.
Note also that Westminster Hall sessions take place at the same time as Commons sessions, which of course are more important.