There was supposed to be a fundraising dinner in Lakewood during the Nine Days for some benefit called "the good of Clal Yisrael".

I don't know what that means, but it seems this is a backdoor way of raising money for the yeshiva BMG in Lakewood. I don't know why they need to do it like this and can't raise explicitly for Lakewood, but this besides the point.

The dinner was set to be an uppity dinner with seven courses of gourmet meat dishes, and obviously open exclusively to a select list of invited guests.

Rav Malkiel Kotler, Rosh Yeshiva of BMG, was set to participate in this dinner and was scheduled to be making a siyyum at the dinner.

It seems this created an uproar. How can the Rosh yeshiva participate in such a dinner and make the siyyum, and, for some reason, this is inappropriate - maybe to make a siyyum in order to eat meat during the Nine Days or that he is participating in such a gourmet event, maybe the entire thing being in the Nine Days... it is unclear, but people were upset and the event was changed to a pareve menu.
source: Haredim10

Appropriate or not, I don't know. I would think if the Rosh Yeshiva was participating in it, with an active role, he must have decided it was ok. Perhaps because it is a dvar mitzva, raising money for the yeshiva or whatever the good cause is, or maybe for other reasons. I find it interesting that the people do not follow the lead of the Rosh Yeshiva, especially in such a town as Lakewood where, I would think  fealty to the gedolim and the local rosh yeshiva is of utmost priority, but basically tell him what he can and cannot do - what is appropriate for him to do and what is not.