I was there for that Mass that day. I was completely confused as to why they would switch things up on such an important liturgical day.
The fact that you were there and yet you were completely confused
adds weight to the impression that they did not explain what they
were doing, because if they had explained it so as to be understood,
then the people who were there (like you!) would have known their
reason(s) and they would not be confused.
Now, there could be mitigating circuмstances, such as perhaps you
had arrived just after someone made an announcement from the pulpit
before Mass, and you had not somehow managed to speak to anyone
who had been there to hear that, because you had stayed after Mass
to pray your thanksgiving and by the time you got up to leave, all
those who had known the answer you sought had already gone away.
Or whatever.
But in all likelihood, the more probable state of affairs is, that there
had been no attempt to explain what the reason was for changing the
Mass from what the calendar indicates (depending, of course, on
which calendar is being used!) to this dedication of the cathedral
liturgy.
Which reminds me, you can be really sure that the diocese cathedral
was not using the prayers for Mass of the Common of the Dedication
of a Church that is found in the 1962 Missal of John XXIII.
Consequently, how can this "L" or the SSPX representative claim
that this "SWITCH" was really any act of 'unity' with the local
diocese?
To be a true act of 'unity' it should be using the same
liturgy that the diocese is using for the occasion - the NovusOrdo
liturgy, for otherwise, it should be seen as
an act of 'rebellion'
or 'dissidence'.